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Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 1.4 Light offer valuable context and analysis.

WBBSE Class 8 Science Chapter 1.4 Question Answer – Light

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
Reflection of an object occurs due to-
i) refraction
ii) regular reflection
iii) irregular reflection
iv) all of above
Answer:
ii) regular reflection

Question 2.
If ray of light reflects perpendicular on a mirror incident angle becomes
i) 90°
ii) 0°
iii) 180°
iv) 80°
Answer:
i) 90°

Question 3.
If ray of light falls on a mirror at 30^\theta angle the reflected angle becomes-
i) 30°
ii) 90°
iii) 0°
iv) 60°
Answer:
iv) 60°

Question 4.
Virtual image –
i) ean be seen by eyes and reflected on screen ,
ii) can not be seen and can not be reflected on screen
iii) can be seen but can not be reflected on screen
Answer:
iii) can be seen but can not be reflected on screen

Question 5.
Shape of reflection created on plane mirror-
i) is of smaller size than the actual object
ii) is of larger size than the actual object
iii) is same as the object
Answer:
iii) is same as the object

Question 6.
If incident ray and reflected ray falls perpendicular on each other then refelected angle becomes-
i) 90°
ii) 45°
iii) 60°
iv) 180°
Answer:
ii) 45°

Question 7.
White light is mixer of how many colours-
i) 7
ii) 2
iii) 4
iv) 10
Answer:
i) 7

Question 8.
Which of the following series does not have lateral inversion-
i) A, B, C
ii) M, N, O
iii) X, A, O
Answer:
iii) X, A, O

Question 9.
If two plane mirrors are placed at a right angle then reflection number of that object weuld be-
i) 2
ii) 3
iii) 4
iv) 5
Answer:
ii) 3

Question 10.
What are the two marginal colours of a spectrum?
i) red and violet
ii) red and blue
iii) violet and blue
Answer:
i) red and violet

Question 11.
Spectrum occurs due to-
i) reflection
ii) refraction
iii) dispersion
Answer:
iii) dispersion

Question 12.
Distance between an object and mirror is 15 cm. If the object is brought 2 cm nearer the mirror then what will be distance between reflection and object-
i) 13 cm
ii) 4 cm
iii) 26 cm
iv) 36 cm
Answer:
i) 13 cm

Question 13.
We can see sun before sunrise and after sunset in atmosphere because-
i) refraction occurs
ii) reflection occurs
iii) dispersion occurs
Answer:
i) refraction occurs

Question 14.
In internal full reflection-
i) incident angle > reflected angle
ii) incident angle < reflected angle
iii) incident angle = reflected angle
Answer:
iii) incident angle = reflected angle

Question 15.
The optical illusion in desert is called-
i) mirage
ii) halucination
iii) imagination
Answer:
i) mirage

State whether True or False : (1 mark for each question)

1) A real source of light is sun.
2) Virtual image can be seen by eyes and reflected on screen.
3) Refrective index of diamond with respect to air is very low.
4) The image formed in a mirror is a virtual image.
5) Periscopes are used in submarine.
6) Mirrage formed in a desert can be obtained on screen.
7) In total internal reflection the image is much brighter.
8) Shape of reflaction created on plane mirror is of smaller size than the actual size .
9) Spectrum occurs due to dispersion.
10) If the ray of light falls on a mirror at 30° angle the reflected angle becomes 90⁶.
11) Convex lens is used in magnifying glass.
12) An unreal source of light is moon.
13) Two marginal colours of the spectrum are red and blue,
14) The angle of refraction becomes greater than the angle of incidence.
15) Critical angle of diamond with respect to air is very high.
Answer:
1) true
2) false
3) false
4) true
5) true
6) false
7) true
8) false
9) true
10) false
11) true
12) true
13) false
14) true
15) fale

Fill in the blanks : (1 mark for each question)

1. In reflection angle of incidence and angle of reflection is always ______.
2. Irregular reflection follows the two rules of ______.
3. ______ reflection does not form any image.
4. Plane mirror forms ______ image.
5. On a screen of cinema _______ images are formed.
6. An object is 15 cm away from mirror. The reflection formed will be _____ distant from mirror:
7. If an object is kept between two parallel mirrors ______ images are formet’.
8. If an object is kept between two mirrors which are inclined at right angle _______ images are fomed.
9. To form image on cinema screen ______ is used.
10. Virtual inage formed by convex lens is always ______ in respect of the object.
11. ______ object does not have any hateral invesion.
12. In splitting of white light, ______ light deviates the least.
13. Prism does not create any _______, only separates the band of colours present in white light.
14. A _____ is formed by the dispersion of sunlight by tiny drops of water present in the air:
15. To create virtual image by convex lens the object should be kept _____ the focus length.
16. Convex lens is used in ____.
17. Dispersion of white light is done by _______.
18. When a ray of light travels from denser medium to a rerer medium, the angle of regration is _____ than the angle of incidence.
19. When a ray of light strikes at the surface of seperation of the two media at right angle, the angle If refraction is ______.
20. Velocity of light in water _______.
Answer:
1) same
2) reflection
3) irregular
4) virtual
5) numerous
6) 15 cm
7) numerous
8) three
9) convex
10) inverted
11) Symmetrical
12) red
13) colour
14) rainbow
15) outside
16) magnifying glass
17) prism
18) more
19) zero
20) 3 × 10⁸ m / s.

Very Short Questions & Answers : (1 mark for each question)

Qustion 1.
What is light?
Answer:
Light is a kind of energy, which after rearhing our eyes creates a sensation to view things.

Qustion 2.
How much time it takes light to reach from sun to earth?
Answer:
It takes 8.3 minutes to reach light from sun to earth.

Qustion 3.
Name a real and unreal source of light.
Answer:
A real source of light is sun and an unreal source of light is moon.

Qustion 4.
Name an instrument which is made using the principal of reflection of light.
Answer:
By using the principal of reflection of light periscope instrument is made.

Qustion 5.
In a plane mirror if a ray of light reflects at 35° angle then what will be the value of reflected angle?
Answer:
The value of reflected angle would be 35°.

Qustion 6.
If a ray of light strikes a mirror perpendicularly what will be the value of reflected angle?
Answer:
The value of reflected angle would be 0°.

Qustion 7.
Which property of light is proved in a pin-bole camera?
Answer:
The property that light travels in a straight line is proved in a pin-hole camera.

Qustion 8.
In what kind of surface regular reflection occurs?
Answer:
Regular reflection occurs in smooth and polished surface.

Qustion 9.
In what kind of surface irregular reflection occurs?
Answer:
Irregular reflection occurs in rough surface.

Qustion 10.
What will be the critical angle of diamond with respect to air?
Answer:
The critical angle of diamond with respect to air is 24.5°.

Qustion 11.
In internal reflection light reflects from which medium to which medium?
Answer:
In internal reflection light reflects from denser medium to rarer medium.

Qustion 12.
Name a natural phenomena which is created due to internal reflection?
Answer:
‘Mirage’ is a natural phenomena which is created due to internal reflection.

Qustion 13.
What is absolute refractive index?
Answer:
The absolute refractive index of a medium is difined as the ratio of the speed of light in vacuum (or air) to the speed of light in that medium.

Qustion 14.
Is Mirage a virtual reflection or a real reflection?
Answer:
Mirage is a virtual reflection.

Qustion 15.
When light enters a denser medium from a rarer medium how it changes its direction?
Answer:
Light moves to wards the normal.

Qustion 16.
When light enters a rarer medium from a denser medium how it changes its direction?
Answer:
Light moves aways from the normal.

Qustion 17.
What type of image is created in a plane mirror?
Answer:
Virtual image is created in a plane mirror.

Qustion 18.
What type of reflection occurs on the page of a book?
Answer:
Irregular reflection occurs on a page of a book.

Qustion 19.
In what kind of reflection image is formed?
Answer:
In regular reflection image is formed.

Qustion 20.
What type of reflection can not be taken on a screen?
Answer:
Virtual reflection can not be taken on a screen.

Short Questions & Answers : (2 marks for each question)

Qustion 1.
What are the essential conditions for the total internal reflection?
Answer:
There are two necessary conditions for the total internal reflection :
i) The light must travel from a denser to a rarer medium.
ii) The angle of incidence must be greater than the critical angle for the pair of media.

Qustion 2.
What is meant when it is said that the critical angle of water with respect to air is 49° ?
Answer:
The critical angle of water with respect to air is 49° then value of refracted angle would be 90° or one right angle.

Qustion 3.
What is meant when it is said that the critical angle of diamond with respect to air is 24.4° ?
Answer:
The critical angle of diamond with respect to air is 24.4° means when ray of light travels from diamond to air then if value of incident angle is 24.4° then value of refracted angle would be 90° or one right angle.

Qustion 4.
What is critical angle?
Answer:
Critical angle is the angle of incidence in the denser medium corresponding to which the angle of refraction in the rarer medium is 90°.

Qustion 5.
On what factors the value of critical angle depends?
Answer:
The value of critical angle depends on two following factors:-
i) nature of the two media that means the refractive index of the media
ii) the colour of light.

Qustion 6.
What is the refraction of light?
Answer:
The change in direction of the path of light, when it passes from one transparent medium to another transparent medium, is called refraction. The refraction of light is essentially a surface phenomenon.

Qustion 7.
What is real image?
Answer:
The images that can be cast on screen are said to be real image. Rays of light coming from a certain point after reflection or refraction if meet at a point, then the second point is known as the real image of the first one.

Qustion 8.
What is virtual image?
Answer:
The images that can not be cast on screen are virtual images. Rays of light coming from a certain point after reflection or refraction if it seems to come from another point, then the second point is said to be the virtual image of the first point.

Qustion 9.
Write down the laws of reflection.
Answer:
i) The angle of incidence is equal to the angle of reflection.
ii) The incident ray, the reflected ray and the normal at the point of incidence. lie in the same plane.

Qustion 10.
Write down the laws of refraction.
Answer:
i) The incident ray, the refracted ray and the normal at the point of incidence, all lie in the same plane.
ii) For refraction of an obliquely ray of incidence of light of any given colour in a given pair of optical media irrespective of the magnitude of angle of incidence and angle of refraction, the refractive index is a constant.

Qustion 11.
What is total internal reflection of light?
Answer:
When a ray of light travels obliquely from a denser medium to a rarer medium, if the angle of incidence becomes greater than the critical angle of the media, the ray of light returns to the first media getting reflected to the surface of separation of the two media. The incident is known as total internal reflection of light.

Long Questions & Answers : (3 marks for each question)

Qustion 1.
Write the properties of real image?
Answer:
i) Real image is inverted with respect to the object.
ii) A photograph of a real image can be taken.

Qustion 2.
Write the properties of virtual image.
Answer:

1. A virtual image is seen with eyes but can not be obtained on a screen.
2. A virtual image is erect with respect to the object.
3. Virtual image formed on a plane mirror had lateral inversion.

Qustion 3.
Why do water on an aurum leaf appear glittering?
Answer:
From air light enters into the drop of water that moves on the aurum leaf. When rays of light try to come out again in air, it appears on the surface of separation of water and air with angle of incidence, more than the critical angle of the two media. As a result, total internal reflection takes place there. The emergent rays then reach the viewer’s eyes and the viewer finds the area glittering.

Qustion 4.
Why does diar ond look shiny?
Answer:
Refractive index of diamond with respect to air is very high. So, eritical angle of diamond with respect to air is very low only 24.5°. Diamond is cut in such a way that when a ray of light attempts to emerge for diamond, the angle of incidence exceeds the magnitude of eritical angle of diamond in air. As a result, total internal reflection occurs and diamond look shiny.

Qustion 5.
Why stars twinkle?
Answer:
Stars are very far away from earth. So the light which emits from star passes through different layers of air. Continuous change in density and refractive index of the air take place due to continuous change of temperature. As a result, the direction of light changes every moment while passing through the succesive air layers. As a result the star seems twinkling to the eye of viewer.

Qustion 6.
Distinguish between real image and virtual image.
Answer:

Real image	Virtual image
1) A real image is formed due to actual intersection of the reflected rays.	1) A virtual image is formed when the reflected rays meet if they are produced back wards.
2) A real image can be obtained on a screen.	2) A virtual image can not be obtained on a screen.
3) A real image is inverted with respect to the object.	3) A virtual image is erect with respect to the object.

Qustion 7.
Which of the following reflections are real image or virtual image, Give reasons.
i) Image on cinema screen,
ii) Image formed on still water of pond.
iii) Image formed on photography plate.
iv) Image formed by concave lens.
Answer:
i) Image on cinema screen is real image as it is obtained on screen.
ii) Image formed on still water of pond is virtual as it cannot be obtained on screen.
iii) Image formed on photographic plate is real as it can be seen as photograph.
iv) Image formed by concave lens is virtual as it cannot be obtained on screen.

Qustion 8.
Distinguish between the total internal reflection and reflection from a plane mirror.
Answer:

Total internal reflection	Reflection from a plane mirror
1) It takes place only when light passes from a denser medium to a rearer medium at an angle of incidence greater then the critical angle for that pair of media.	1) It takes place when light is incident on a plane mirror from any medium at any angle of medium.
2)The entirfe light is reflected.	2) Only a part of light is reflected while rest is refracted and absorbed.
3) There is no loss of energy. The energy of reflected ray is same as that of incident ray.	3) There is a loss of energy. The energy of reflected ray is less than that of the incident ray.
4)The image is much brighter.	4) The image is less bright and the bright ness as the silvering on miror becomes old and rough.

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 3 Know About Some Common Gases offer valuable context and analysis.

WBBSE Class 8 Science Chapter 3 Question Answer – Know About Some Common Gases

Hands-on Activity :

Answer (See Text-book, page-124)

Answer:

Answer (See Text-book, page-125)

Fill up the blanks (See Text-book, page-131-132)
Answer :
A. 1. Zn + dilute H₂ SO₄ → ZnSO₄ + H₂
2. Mg + dilute HCl → MgCl₂ + H₂
3. Fe + dilute H₂ SO₄ → Fe₂(SO₄)₃ + H₂
4. Al + dilute HCl → Al₂ Cl₂ + H₂

B. 1. Na + H₂ O (cold water) → NaO + H₂
2. Ca + H₂ O (cold water) → CaO + H₂
3. Mg + H₂ O (boiling water) → MgO + H₂
4. Al + H₂ O (boiling water) → Al(OH)₂ + H₂
5. (red hot) Fe + H₂ O(. steam) → Fe₂ O₃ + H₂

C. 1. Zn + NaOH (concentrated solution) → Na₂ ZnO₂ + H₂
2. Al + NaOH (concentrated solution) + H₂ O → NaAlO₂ + H₂
Si + 2 NaOH + H₂O = Na₃ SiO₃ + 2 H₂

D. Water acidified with sulphuric acid (H₂O) → O₂ + H₂
E. CaH₂ + 2H₂O → Ca(OH)₂ + H₂
LiH + H₂O → LiOH + H₂

Class 8 Science Chapter 3 Question Answer West Bengal Board – Know About Some Common Gases

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
Catalyst enzyme breaks down hydrogen peroxide into-
i) oxygen
ii) hydrogen
iii) water and oxygen
iv) water and hydrogen
Answer:
iii) water and oxygen

Question 2.
Number of isotopes in oxygen-
i) three
ii) four
iii) two
iv) five
Answer:
i) three

Question 3.
Freczing point of liquid oxygen is–
i) -183° C
ii) -100° C
iii) -118° C
iv) -218° C
Ans:
iv) -218° C

Question 4.
Oxygen is-
i) colourless
ii) odourless
iii) tasteless
iv) all of the above
Answer:
iv) all of the above

Question 5.
Alkaline potassium pyrogallate solution absorbs oxygen and turns-
i) white
ii) brown
iii) red
iv) green
Answer:
ii) brown

Question 6.
Water is made up of –
i) hydrogen
ii) oxygen
iii) hydrogen and oxygen
Answer:
iii) hydrogen and oxygen

Question 7.
Which of the following is true-
i) hydrogen is the lightest gas
ii) hydrogen is heavier than air
iii) oxygen is lighter than air
iv) hydroge is equal to air in weight
Answer:
i) hydrogen is the lightest gas

Question 8.
Which of the following is not fertilizer?
i) urea
ii) ammonium sulphate
iii) ammonium nitrate
iv) atomic oxygen
Answer:
iv) atomic oxygen

Question 9.
Which of the following is chemical propertiy of hydrogen?
i) not inflammable
ii) inflammable
iii) formation of oxide
iv) not diatomic
Answer:
ii) inflammable

Question 10.
Which of the following material is required for preparation of hydrogen gas?
i) manganese dioxide
ii) solution of hydrogen peroxide
iii) impure zine granules
iv) pure zinc granules
Answer:
iii) impure zine granules

State whetherTrue or False : (1 mark for each question)

1. Oxyzen is slightly heavier than air:
2. Atomic oxygen is a powerful oxidizing agent.
3. Hydrogen is indispensable in manufacturing nitric acid.
4. Oxygen is completely soluble in water.
5. Oxygen can combine directly with most of the metals and non-metals.
6. Hydrogen is heavier than air.
7. Hydrogen is used in production of ammonia.
8. Hydrogen gas does not help in burning.
9. A woulfe bottle is necessary for preparation of oxygen.
10. Manganese dioxide is required for preparation of hydrogen.
Answer:
1. true
2. true
3. fa’se
4. false
5. truc
6. false
7. true
8. true
9. false
10. false

Fill in the blanks : (1 mark for each question)

1. Hydrogen is necessary in many ___ industries.
2. The industrial world gets its requirement of oxygen from _____.
3. Oxygen-dependent processes do generate more ______ but there are some disadvantages.
a. Aluminium reacts with oxygen and produce ______.
5. At normal or low temperature Au, Ag can absorb______.
6. Delute solution of hydrogen is required for preparation of ______.
7. Colourless nitric oxide gas is oxidized to brown _______ in contact with oxygen.
8. The main use of hydrogen is in the production of _____.
9. Air is about 14.4 times havier than ______.
10. Hydrogen does not help in burning but it is ______.
11. Platinum can absorb ______ gas at normal temperature.
Answer:
1. chemical
2. air
3. energy
4. aluminium oxide
5. oxygen
6. oxygen
7. nitrogen dioxide
8. ammonia
9. hydrogen
10. inflammable
11. hydrogen
12. chemical

Match the following : (1 mark for each question)

a) Match the column A with column B.

Column A	Column B
a) Oxygen is slightly	i) manufacturing nitric acid.
b) Atomic oxygen is a powerful	ii) from vegetable oils.
c) Alkaline potassium pyrogallate solution	iii) insoluble in water.
d) Oxygen is indespensable in	iv) oxidizing agent.
c) hydrogen is used to produce edible fats	v) is 218°C
f) Hydrogen is almost	vi) hydrogen is colourless and tasteless.
g) Freezing point of liquid oxygen	vii) heavier than air:
h) Oxygen is	viii) react with oxygen.
i) Under normal coditions	ix) absorbs oxygen and turns blue.
j) Aluminium and rine	x) not inflammable.

Answer:
a) Oxygen is slightly heavier than air.
b) Atomic oxygen is a powerful oxidizing agent.
c) Alkaline potassium pyrogallate solution absorbs oxygen and tums blue.
d) Oxygen is indespensable in manufacturing nitric acid.
e) hydrogen is used to produce sdible fats from vegetable oils.
1) Hydrogen is almost insoluble in water.
g) Freezing point of liquid oxygen is -218° C.
h) Oxygen is not inflammable.
i) Under normal coditions hydrogen is colourless and tasteless.
j) Aluminium and zinc react with oxygen.

Very Short Questions & Answers : (1 mark for each question)

Question 1.
What does the decomposition of H₂ O₂ produce?
Answer:
Water and oxygen.

Question 2.
What is the chemical symbol of hydrogen?
Answer:
H₂

Question 3.
What is the specific gravity of hydrogen?
Answer:
It is the lightest of all gases with a specific gravity of 0.0695 .

Question 4.
How is hydrogen detected?
Answer:
It can be detected by chemical analysis.

Question 5.
Is hydrogen water soluble?
Answer:
No.

Question 6.
What is the specific gravity of oxygen?
Answer:
Specific gravity of oxygen is 1.105

Question 7.
What is the chemical symbol of oxygen?
Answer:
O₂

Question 8.
Is oxygen flamable?
Answer:
No. Oxygen alone will not burn.

Question 9.
When the oxygen level in air considered to he dangerous?
Answer:
When oxygen level falls below 16 %.

Question 10.
What element in the air is essential for life?
Answer:
Oxygen.

Short Questions & Answers : (2 marks for each question)

Question 1.
Write two advantages of having oxygen in air.
Answer:
Oxygen is necessary for respiration in living organisms. Oxygen reacts with food and releases energy.

Question 2.
What happens when Oxygen reacts with non-metals?
Answer:
Oxygen reacts with non-metals such as carbon. sulphur and phosphorus to form acidic oxides. C + O₂ → CO₂ \quad S + O₂ → SO₂

Question 3.
Why oxygen is called acid producer?
Answer:
The non-metals, on combustion with oxygen. produce oxides. These oxides produce acid when they react with water. So these oxides are called acidic oxides.

Question 4.
Mention some metals which absorb oxygen.
Answer:
At normal or low temperature, Au, Ag, Pt. Pb etc. can absorb oxygen. i.e can bind oxygen weakly at their surface. On heating the metal, oxygen is released.

Question 5.
What are the materials required for preparation of oxygen gas from hydrogen peroxide?
Answer:
i) delute solution of hyfrogen peroxide
ii) manganese dioxide
iii) a jute stick
iv) a test tube
v) a test tube holder

Question 6.
What are the materials required for preparation of oxygen gas from sodium peroxide?
Answer:
i) sodium peroxide
ii) distilled water
iii) conical flask
iv) a cork with two holes
v) a dropping funnel
vi) a bent delivery tube
vii) a gas jar

Question 7.
What are the materials required for preparation of oxygen gas from potasium chlorate?
Answer:
i) potassium chlorate,
ii) manganese dioxide free from carbon,
iii) a hard glass test tube,
iv) a cork with a bore,
v) a delivery tube,
vi) a stand,
vii) a gas tough,
vii) a water pot.

Question 8.
What are the materials required for laboratory preparation of hydrogen gas?
Answer:
i) impure zinc ganules
ii) dilute sulphuric acid, distilled water
iii) woulf bottle
iv) thistle funnel
v) bored cocks for wolf bottle
vi) delivery tube
vii) rubber tube
vii) grease.

Long Questions & Answers : (3 marks for each question)

Question 1.
What are the advantages of having oxygen in air?
Answer:
Oxygen is necessary for respiration in living organisms. Oxygen reacts with food and releases energy. Generation of energy from intra-cellular glucose is faster, easier and more efficient with oxygen than without it. It supports combustion. There can be no fire without oxygen.

Question 2.
What vital role oxygen play during respiration of living beings?
Answer:
The role of oxygen in the respiration of animals or plants is extremely vita!. The most important process associated with the respiration of animals is the combination of oxygen i.e combustion of simple ingradient of the carbonaceous food. As a result, the required energy is produced in the body. For example, glucose the simple ingredient of carbohydrate gets oxidised and produce energy.

Question 3.
Write down some absorber of oxygen.
Answer:
Absorber of oxygen are:
i) At normal or low temperature, Au, Ag, Pt, Pb etc. can absorb oxygen, i.e can bind oxygen weakly at their surgace. On heating the metal, oxygen is released.
ii) Alkaline potassium pyrogallate solution absorbs oxygen and turns brown.
iii) Ammoniacal cuprous chloride solution absorbs O₂ gas quickly and turns blue.

Question 4.
Write some uses of oxygen.
Answer:
i) Oxygen is used in breathing support systems by patients who cannot get enough oxygen from air due to some health problems.
ii) Oxygen is used to remove the impurities of crude iron. In this way, millions of tonnes of steel are produced.
iii) Oxygen is indepensable in manufacturing nitric acid (HNO₃) and sulphuric acid (H_{2 4}).

Question 5.
Write the way of preparation of oxygen in laboratory with the equation.
Answer:
In laboratory Oxygen can be prepared by heating together four parts of potassium chlorate and one part of manganese dioxide. Manganese dioxide acts as the catalyst. It is not consumed in the reaction. It only help potassium chlorate to decompose faster and at lower temperature. The equation of the reaction for such production of oxygen is-

2 KClO₃ + [MnO₂] → 2 KCl + 3 O₂ + [MnO₂]

Question 6.
Write some use of hydrogen.
Answer:
a) Hydrogen is used to produce ammonia, which is use in the production of urea fertiliser.
b) It is used to produce various petrochemicals.
c) For the production of hydrogenated vegetable oils, we need hydrogen.

Question 7.
Write some physical properties of oxygen.
Answer:
Some properties of oxygen are-

1. It is colourless, tasteless, odourless gas at ordinary temperature.
2. It is slightly heavier then air : Its denisty at normal temperature and pressure is 1.428 gram per litre.
3. It is slightly soluble in water: Solubility of oxygen at 0° C and 1 atm pressure is 14.8 mg per litre.
4. Freezing point of liquid oxygen is -218° C and boiling point is -183° C.
5. Oxygen has three isotopes, namely, , and though the natural abundance of the last two is very low.

Question 8.
Write two physical properties and two chemical properties of IIydrogen.
Answer:
Two physical properties of Hydrogen are-
1) Under normal conditions, hydrogen is colourless odourless. tasteless gas.
2) Hydrogen is the lightest gas. Air is about 14.4 times heavier than hydrogen.

Two chemical properties of Hydrogen are-
1) Combustibility: Hydrogen does not help in burning but it is inflammable. If a mixture of hydrogen and oxygen is burit into flame. steam is produced

2 H₂ + O₂ → 2 H₂ O

2) Reduction: Hydrogen has special attraction for oxygen. Hydrogen acts as reducing agent for its high affinity towards oxygen. Reddish-brown copper is produced by reduction of hot cupric oxide by a current of hydrogen gas. Hydrogen is oxidised to water

CuO + H₂ → Cu + H₂ O.

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 5 Analysis of Natural Phenomena offer valuable context and analysis.

WBBSE Class 8 Science Chapter 5 Question Answer – Analysis of Natural Phenomena

Fill up the blanks : (See Text Book Page 172)

Name of the disease	How transmitted	Responsible germ	Means to avoid the disease
1. Cholera	Uncovered food unclean environment	vibrio cholera	taking pure food & drink
2. Maleria	biting of mosquito	Plasmodium vivax	avoid mosquito biting
3. Plague	biting of rats	Yersinia pestis	avoid rat biting
4. AIDS	body fluid & mucous	HIV virus	consciousness
5. Kala Azar	carrier sand fly	Leishmania donovani	consciousness

Write down what problems may be faced for the absence of proper food habits arid right life style.

Food habit and life style	Problems likely to be faced
1. Intake of excess carbohydrate	risk of heart disease
2. Intake of excess carbohydrate	risk of diabetes
3. Staying awake at night and insufficient sleep	headache, blood pressure
4. Working with computer for long duration without interruption	spondylities, headache
5. Smoking and intake if intoxicating substances	risk of cancer
6. Excessive use of mobile phone	eye problem, cancer

Class 8 Science Chapter 5 Question Answer West Bengal Board – Analysis of Natural Phenomena

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
During thunder the air —
i) vibrates
ii) radiates
iii) attracts violently
Answer:
i) Vibrates

Question 2.
The height of a storm cloud is generally —
i) 3-4 km.
ii) 7-8 km.
iii) 12-13 km.
iv) 17-18 km.
Answer:
iii) 12-13 km.

Question 3.
The lighting conduction is buried at least —
i) 5-6
ii) 10-12 P
iii) 15-18
iv) 20-22 feet deep into the ground.
Answer:
i) 5-6 feet

Question 4.
An epidemic disease is —
i) heart disease
ii) Cholera
iii) headache
iv) skin disease
Answer:
ii) Cholera.

Question 5.
Mosquito-born fatal disease dengue first broke out in Kolkata in the year —
i) 1986-1987
ii) 1982-83
iii) 1990-92
iv) 1963-64
Answer:
iv) 1963-64

Question 6.
Cholera generally causes from —
i) polluted air
ii) polluted water
iii) mosquito
iv) polluted food
Answer:
ii) Polluted water.

Question 7.
The word ‘Malaria’ means —
i) bad water
ii) bad light
iii) bad air
iv) bad soil
Answer:
iii) Bad air

Question 8.
The carrier of Malaria disease —
i) fly
ii) Mouse
iii) Mosquito
iv) lice
Answer:
iii) Mosquito

Question 9.
The medicine of Kalazar was invented by —
i) Galielio
ii) Jagadish chandra Bose
iii) Satyandranath Dtitta
iv) Upendranatk Brahmachari
Answer:
iv) Upendranath Brahmachari

Question 10.
Blood appears in stool in —
i) diarrhoea
ii) smallpox
iii) plague
iv) malaria
Answer:
i) Diarrhoea.

Question 11.
Tuberculosis disease is —
i) waterborne
ii) mosquito-borne
iii) airborne
Answer:
iii) airborne.

Question 12.
Treatment of Tuberculosis is called —
i) HOTS
ii) ACTS
iii) GTSS
Answer:
i) DOTS

Question 13.
Types of Hepatitis are —
i) 2
ii) 3
iii) 4
iv) 5
Answer:
iv) 5

Question 14.
The virus responsible for AIDS disease —
i) IVH
ii) HIV
iii) STS
iv) HVP
Answer:
ii) HIV

Question 15.
Another name of small Pox is —
i) Red plague
ii) Kalazar
iii) white plague
iv) green plague
Answer:
i) Red plague

State whether True or False :(1 mark for each question)

1) Lighting inducts the earth with negative charge.
2) Almost even, day at some part of the world lightning occurs due to thunderstorms which are at least 4,000.
3) The clouds become charged to the friction of clouds or that of the water
4) Generally clouds bring in thunderstorms and rain.
5) Clouds are formed by (lie condensation of tater deoplets.
6) The height of a storm cloud is generally 4-5 km.
7) The water droplets became charged when the clouds rise and come down at the time of storm.
8) The lower edges of tite clouds are inducted with positive charge.
9) There is potential difference between the sky and the earth.
10) If there is potential difference, then lightning may occur between two different cloud or parts of same cloud.
Answer:
1) true
2) false
3) false
4) true
5) true
6) false
7) true
8) false
9) true
10) true

Fill in the blanks : (1 mark for each question)

1) The part of the train which is in contact with the electric line is called ________
2) The electrical cells used in radios or torches is called ________
3) In our country, thunderstorms and highlighting seldom occur in ________
4) In an atom (lie electron and the proton are ________ particles.
5) Atoms arc uncharged because the number of protons and electrons in atom is ________
6) If an electron is released from on atom, then the atom becomes a ________
7) In winter if plastic comb is used for combing hair, it acquires ________ charge.
8) ________ is a high-energy electric discharge and it can cause great harm.
9) The flow of electric charge is called an ________.
10) Lighting is that cell in nature which maintains the ________ of electric charge high up in the sky and on earth.
Answer:
1) pantograph
2) dry cell.
3) winter
4) electrically charged
5) equal
6) positive ion
7) negative
8) lighting
9) electric current.
10) potential difference.

Very Short Questions & Answers : (1 mark for each question)

Question 1.
Which cells are called dry cell?
Answer:
The electricals cells used in radios or torches are called dry cell.

Question 2.
What is pentograph?
Answer:
The part of the train which is in contact with the electric line is called pentograph.

Question 3.
Who did experiment on electric spark?
Answer:
Famous scientist Benjamin Franklin.

Question 4.
Which charge is inducted in the lower edges of the clouds?
Answer:
Negative charge.

Question 5.
Which charge is inducted the upper edges of the clouds?
Answer:
Positive charge.

Question 6.
What is the reason that opposite charges accumulate at different edges of the clouds?
Answer:
Potential difference between the sky and the earth. ,

Question 7.
What is the work of lighting conductor?
Answer:
Lighting conductions a device that protects houses and electrical equipments within the house.

Question 8.
What is an epidemic?
Answer:
When hundreds of people die at the same time in every year due to out break of a fatal disease, then that disease is declared as an epidemic.

Question 9.
Write name of some epidemic diseases.
Answer:
Some epidemic diseases are — Malaria, Aids, Influenza, Dengue etc.

Question 10.
Which diseases occur in spring season?
Answer:
The onset of spring sees a spirit in diseases like Measles and Chicken Pox.

Question 11.
Which diseases are common in winter season?
Answer:
Infection of the upper tracts of the respiratory organ is generally common in winter months.

Question 12.
When stomach infection is usually high?
Answer:
Stomach infection is usually high in summer.

Question 13.
What is the cause of Cholera disease?
Answer:
Cholera disease is generally caused from polluted water, uncovered and fly infected food and unhyginenic environment.

Question 14.
Name the germ of disease Cholera.
Answer:
Vibrio cholerae.

Question 15.
Name the germ that female anopheles mosquito carries.
Answer:
Plasmodium vivax or Plasmodium falciparum.

Question 16.
Which mosquito carries the germ of Dengue?
Answer:
A type of mosquito called Aedes Egypt carries the germ of Dengue.

Question 17.
Name the bacteria resposible for Plague.
Answer:
Yersimia pestis is responsible for plague.

Question 18.
Name the type of fly which carries the bacteria from body of rat afflicted with plague.
Answer:
Xenopsyllachopis.

Question 19.
Who invented the vaccine of plague?
Answer:
In 1987, Waldemar Haffkine invented the vaccine of piague in Bombay.

Question 20.
Name the protozoa and the carrier fly which causes Kalazar.
Answer:
The name of protozoa is Leishmania and the carrier fly is Sand fly.

Question 21.
Who invented the vaccine of small pox?
Answer:
British scientist Edward Jenner invented the vaccine of small pox.

Question 22.
What is SARS?
Answer:
It is an epidemic disease Severe Acute Respiratory Syndrome.

Question 23.
What is DOTS?
Answer:
The deadly disease Tuberculosis is prevented through DOT or Directly Observed Treatment.

Question 24.
Name the bacterium resposible for Tuberculosis.
Answer:
Microbacterium tuberculosis.

Question 25.
How many types of Hepatitis is there?
Answer:
There are five types of Hepatitis A, B, C, D and E.

Question 26.
How A and E types of Hepatitis occur.
Answer:
A and E types of infection is caused by contaminated food and water.

Question 27.
How B, C and D type of Hepatitis occur?
Answer:
B, C and D type of Hepatitis infection occurs through the medium of the body fluid and blood of human.

Question 28.
Which day has been declared by WHO as World Hepatitis Day?
Answer:
World Health Organisation (WHO) has declared 28th July as World Hepatitis Day.

Question 29.
What is the full form of AIDS and HIV?
Answer:
Full form of AIDS is – Acquired Immune Deficiency Syndrome and of HIV — Human Immuno dificieancy Virus.

Question 30.
Name some non-infectious diseases which have assumed epidemic dimensions.
Answer:
Some non-infections diseases such as diabetes, hypertension, cancer, mental illness also have assumed epidemic dimensions.

Short Questions & Answers : (2 marks for each question)

Question 1.
What are electrolytes? Give example.
Answer:
The compounds which are able to conduct electricity in a fused state or in a solution, are called electrolytes. Examples of electrolytes are acid or alkyl solution, aqueous solution of a salt, fused Nacl etc.

Question 1.
What is electricity?
Answer:
Electricity is a form of energy and can, thus, be converted to heat, light and even sound. Electricity is caused due to motion of electric charges, which causes electric current to be generated.

Question 2.
What is static electricity?
Answer:
The accumulation of electrical charges on the surface of a material, usually an insulator or a non-conductor of electricity, gives rise to the concept of static electricity. This electricity is, called ‘static’ because there is no current flowing. However, static electricity can cause sparks, shocks or materials to cling to each other.

Question 3.
What is ion? How it can become positive or negative ion?
Answer:
If in an atom number of protons and number of electrons are equal then that atom is called ion. But if the number of protons exceed the number of electrons then the atom become, a positive ion. If the number of protons is less than that of electrons, then the atom becomes a negative ion.

Question 4.
Write short note on Cholera.
Answer:
This disease generally causes from polluted water, uncovered and fly infected food unhygienic environornent, The body is dehyadrated with bouts of vomiting. The skin becomes foggy and bluish. It is a fatal desease, so proper treatment is must for survival. Cholera is caused by a germ known as Vibrio cholerae.

Question 5.
Write short note on Malaria,
Answer:
Malaria is a mosquito carried discease. A female anopheles mosquito carries a germ called Plasmodium vivax or Phasmodium falciparum and injects it in the blood stream of a healthy person to cause malaria. High fevers with tremors are a common symptom. Headache and enlargement of splen and liver, joint pain and body ache are other symptoms. If may be fatal if not prompty treated.

Question 6.
Write short note on Dengue,
Answer:
A type of mosquito called Aedes egypti carries the germ of this disease. The germ is known as flavi virus. High fever, headache, joint pain and lowering of platelet count to a dangerous level causing obstruction and coagulation of blood are the common incidents. Oozing of the blood is the main symptom of the disease, by destroying the white blood corpuscles (WBC). Unless treated in time, dengue can be fatal.

Question 7.
Write short note on Plague.
Answer:
This disease is transmited by rats to the human body. A bacterium called Yersinia pestis is responsible for this disease. The main symptoms are lung infection, blood clothing, severe pain from swelling of the lymph gland, vomiting and oozing of blood with cough.

This disease can be transmitted by various means such as sneezing, direct body contact, touching infected soil and even from bites of flying insects. A type of fly called Xenopsylla cheopis carries the bacteria from body of rat afflicted with plague.

Question 8.
Write short note on Tuberculosis.
Answer:
Mycobacterium tuberculosis is responsible for this disease. This bacterium attacks the lungs of human beings. Tuberculosis can occur in intestine and bones. This disease is highly infectious. Infection can occur from cough and mucous an even through spits and saliva.

Symptoms of the disease are severe cough, with the letting of blood, profuse sweating and gradual loss of weight. It can be cured by DOTS or directly observed treatment, short course.

Long Questions & Answers : (3 marks for each question)

Question 1.
Explain how cloud forms and bring rain?
Answer:
The air containing water vapour rise upward. Air from surrounding region rushes toward this place and also starts to move upward. In the upper layer of the atmosphere the temperature and pressure of air is less. The water vapour rises up into the sky and condenses. As a result the vapour converts into droplets thus cloud is formed.

A time comes when the water droplets become so heavy that they come down due to gravity. Even the winds of high speed in the upper layer of the atmosphere cannot stop the downward motion of water droplet. By this time the formation of clouds for thunderstorm has completed. Then the wind also starts to go downward. In such a situation rain and storm begin on earth.

Question 2.
Explain how lightning and thunder occur.
Answer:
The lower portion of a cloud generally carries negative charges and the upper portion carries positive charges. Air of the atmosphere acts as an insulator and the charges do not flow. When a huge amount of charge builds up and when clouds with unlike charges come close to each other, the insulation of air breaks down and there is a heavy electric discharge between two cloud having opposite charges or between a charged cloud and the ground.

This causes a large amount of energy to be in the form of heat, light and sound. The flash of light is the lighting we see, and the large amount of heat causes expansion and vibration of air resulting in the thundering sound.

Question 3.
Explain how lightning causes harm and precautions we can take during lightning.
Answer:
Lightning can cause great harm. It can kill human beings and animals, destroy buildings, melt metals and also cause fires. We should take the following precautions during lightning —

• We should try to take shelter inside a building, or even in a car or a truck. We should avoid taking shelter in sheds with metal roofing.
• Do not stand under a tree. As lighting tends to strike tall objects, the true has a possibility of getting struck by lightning.
• Do not run across an open field. Also, do not stand on high ground. Squat down on the low-lying ground if safe place cannot he found.

Question 4.
What is a lightning conductor, how it works?
Answer:
Lightning conductor is a device that protects houses and electrical equipments within the house. A metallic rod is installed at the highest point of the building. At the highest point of the rod, there exist some small skewers. A wide metal plate is buried at least 5-6 feet deep into the ground. A thick wire of good conductor is connected to the metal plate and the rod.

This system protects the house from lighting. The high voltage of current produced in lightning is transferred to the earth through the easy route of the wire. Even if lightning strikes the house, no damage occurs to the house.

Question 5.
Define the types of epidemic
Answer:
Types of epidemic are —

• Epidemic front common source : This types of epidemic is caused by any disease creating germ but not always (like poisoning of water, air, food or soil. Typical examples are Bhopal Gas Tragedy or Japanis Minamata disease).
• Epidemic from infection : Epidemic of this type is directly transmitted by one person to the other or through the medium of a living carrier of by infection front the body of living being (Measles, Small Pox, Influenza, Malaria)
• Slowly Infectious epidemic : Lung Cancer, Coronary heart Disease.

Detailed explanations in West Bengal Board Class 7 Science Book Solutions Chapter 5 Human Food offer valuable context and analysis.

WBBSE Class 7 Science Chapter 5 Question Answer – Human Food

(Page no. 145)

Let’s make a list of our daily work from the following pictures.
Answer:

(Page no. 147)

So, what kinds of food (plant/animal) do we eat? Which food component is less or excess in these food items? Discuss with your teachers and fill up the following chart from the discussions later on.

(Page no. 148)

Let’s make a chart showing food components present in different common foods. Take help from your teacher to fill up the following chart.

Food Source	Main Food elements
1. Rice, roti, milk, fruit, potato, sweet potato, honey, sugar, jaggery	Carbohydrate
2. Fish, meat, egg, milk, pulses, cheese, soyabean	Protein
3. Butter, ghee, coconut, groundnut, oil, animal fat. milk, fish	Lipid
4. Drinking water, fruits, vegetables, tea, milk, cooked food	Water
5. Tomato, amla, whole wheat grain, carrot, green vegetables, fruits	Vitamin
6. milk, salt, rice, molasseo, meat, leafy vegetables, milk, fish, pulses	Mineral
7. Mango, apple, oat, papaya, leafy vegetables, whole grains, pulses	Food fibre
8. Tea, ripe mango, ripe papaya, beet, pomegranate, watermelon	Phytochemical.

Page no. 150

Apart from the food items mentioned on the previous page some more are mentioned in the table below. Ask your teacher to know whether these contain carbohydrates or not.

Food	Present/Absent
1. Pumpkin	Present: 7gr./100gr.
2. Raisin             .	Present : 79gr./100gr.
3. Custard-apple	Present: 24gr./100gr.
4. Berry	Present: 14gr./100gr.
5- Egg	Present: 1.1 gr./100gr.
6. Cumin	Present: 44gr./100gr.
7. Curd	Present: 3.4gr./100gr.
8. Cake	Present: 59gr./100gr.
9. Ghee	Absent: 0gr./100gr.
10. Flattened rice	Present: 40gr./100gr.

(Page no. 152)

Apart from the food items mentioned above, some more mentioned in the table below. Ask your teacher to know whether these contain protein or not.

Food	Present/Absent
1. Rice/wheat	Present: 2.7gr./100gr, 12.61 gr./ 100gr.
2. Ghee	Absent: 0.3 8gr./100gr.
3. Groundnut	Present: 26gr./100gr.
4. Sesame	Present: 18gr./100gr.
5. Banana	Present: 1.1 gr./100gr.
6. Mushroom	Present: 3.1 gr./100gr.
7. Suji	Present: 13gr./100gr.
8. Ant eggs	Present: 8.2gr./100gr.

(Page no. 153)

Try to find out if lipid is present in the food mentioned in the table below.

Food / Drink	Present/Absent
1. Fruits and vegetables	Absent
2. Cereals	Absent
3. Tonnedmilk	Absent
4. Popcorn	Absent
5. Potato	Absent
6. Sugarcane juice	Absent
7. Lemon	Absent
8. Wheat, mazie, rice	Absent
9. Mushroom	Present
10. Chicken	Present
11. Dates	Absent

(Page no. 161)

Put the name of food components and their sources in the following table.

Food component	Food
1. Sugar	Rice, wheat, Bazra, potato, beat, carrot, sugar.
2. Protein	Fish, meat. egg. milk, pulse, soyabean, peas.
3. Lipid	Nut. coconut, ghee, butter, oil, fish, fat of meat.
4. Vitamin	Capsicum, tomato, green vegetables, gram, milk
5. Minerals	Green vegetables, food grain, soyabean, fish, meat, egg.
6. Water	All types of rinking water, fruit juice, coconut water
7. Fibre	Cereal, apple, oat, papaya, broccoli, figs, berries.
8. Plant chemical	Tea, cabbage, carrot, tomato, ripe mango

(Page no. 161)

Some physiological problems are mentioned. Which foods are required to prevent these health problems?

Problems	Which food should you have	Which food component will you get
Swollen gums with bleeding	Sour fruits, amla, lemon, guava	Vitamin C
Anaemic condition	Egg. milk, banana, guava	Vitamin B-complex
Weak and curved bones	Egg, milk, butter, cod liver oil	Vitamin-D
Constipation	Vegetables, cabbage, guava	Fibre
Short sight at night	Vegetables, milk, carrot, tomato	Vitamin-A
Ulcer in mouty and tongue	Egg, milk, spinach.	Vitamin B-complex
Wrinkled skin	Carrot, letus. egg, milk, raddish	Vitamin-A
Sudden rise in blood pressure	Small fish, vegetables, fruits	Sodium

(Page no. 162)

There are a few names of food. Try to find out which food components can you get from them. Take help from your teacher, if necessary.

• Ripe mango : Food fibre, sugar, vitamin
• Milk: Protein, vitamin, lipid, minerals
• Nuts : Lipid, vitamin, carbohidrate
• Egg : Protein, vitamin, lipid, minerals
• Guava : Vitamin, minerals, sugar
• Gurd : Vitamin, minerals, sugar
• Tomato : Vitamin, plant chemicals
• Rice : Carbohidrate, vitamin
• Spinach : Vitamin, minerals, foodfibre
• Amla : Vitamin, minerals

(Page no. 166)

Following symptoms develop due to defficiency of different food components. Write down the names of food items that can prevent these diseases.

Symptoms	Defficiencyof food component	Somponents are found in
Bent limbs	Vitamin D	Milk, egg, butter, fish
White spot in iris	Vitamin A	Carrot, egg, milk, curd, letus
Can’t read blackboard	Vitamin A	Carrot, egg, milk, curd, letus
Ulcer on tongue, nouth	Vitamin B Complex	Vegetable, cabbage, milk, green chilli
Swollen face	Protein	Milk, fish, meat, panir, soyabean
Broken nails	Calcium	Milk, amla, lemon, guava
Rough skin	Vitamin A	Carrot, egg, milk, curd, letus

(Page no. 166)

Weight and height of some children and adults are mentioned below. Calculate BMI from it.

Weight (kg)	Height (m)	BMI (weight/height2)	Obese yes/no	Synptoms
62	1.57	25.15	no	normal
66	1.50	29.33	yes	high blood pressure, asthma
72	1.59	28.47	yes	(respiratory problem, diabetes
64	1.62	24.38	no	normal
75	1.60	29.29	yes	high blood pressure, asthma
71	1.58	28.44	yes	knee pain, asthma
72	1.67	25.81	no	normal

Class 7 Science Chapter 5 Question Answer West Bengal Board – Human Food

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
Which is known as instant source of energy ……………………….
i) starch
ii) vitamins
iii) minerals
iv) glucose
Answer:
iv) glucose

Question 2.
Dificiency of iron in our diet casues ……………………….
i) scurvy
ii) anaemia
iii) goitre
iv) blindness
Answer:
ii) anaemia

Question 3.
Plants manufacture food in the form of ……………………….
i) starch
ii) fructose
iii) glucose
Answer:
iii) gluuose

Question 4.
What helps in removing wastes from the body ……………………….
i) water
ii) protein
iii) glucose
iv) phytochemical
Answer:
i) water

Question 5.
Starch is a complex ……………………….
i) mineral
ii) lipid
iii) glucose
iv) carbohydrate
Answer:
iv) carbohydrate

Question 6.
Daily requirement of carbohydrate by an adult is ……………………….
i) 500 gram
ii) 300 gram
iii) 600 gram
iv) 100 gram
Answer:
i) 500 gram

Question 7.
Marasmus is due to the deficiency of ……………………….
i) vitamin C
ii) carbohydrate
iii) fat
iv) protein
Answer:
iv) protein

Question 8.
To get sufficient carbohydrate one should take ……………………….
i) meat
ii) rice
iii) carrot
iv) ground nut
Answer:
ii) rice

Question 9.
What one of the following is the best source of vitamin-A?
i) egg
ii) honey
iii) carrot
iv) pea nut
Answer:
iii) carrot

Question 10.
Fat soluble vitamins are ……………………….
i) A D E and K
ii) B C and D
iii) D B and E
iv) A B and C
Answer:
i) A D E and K.

Question 11.
Vitamin essential for blood clotting is ……………………….
i) A
ii) E
iii) C
iv) K .
Answer:
iv) K

Question 12.
Which one is body-building material?
i) mineral
ii) Protein
ii) fat
iv) sugar
Answer:
ii) Protein

Question 13.
Scurvy disease causes in deficiency of vitamin ……………………….
i) C
ii) B
iii) K
iv) A
Answer:
i) C

Question 14.
Artificial chemical Ajinamoto is used to make ……………………….
i) chocolate
ii) popcorn
iii) momo
iv) tea
Answer:
iii) momo

Question 15.
Trans-fat is present in ……………………….
i) pastry
ii) potato chips
iii) cotton
iv) coffee
Answer:
ii) potato chips

Fill in the blanks : (1 mark for each question)

1. ………….. provides us energy for all life activites.
Answer:
Food

2. Food keeps us healthy and enables us to fight against …………..
Answer:
diseases.

3. In the process of digestion starch a ………….. is broken down into the smallest unit (Glucose).
Answer:
complex carbohydrate.

4. Energy is produced in the cells of the healthy body by break down of …………..
Answer:
glucose.

5. ………….. is caused due to the lack of food fibre in our diet.
Answer:
Constipation

6. The protein that is present in hair and nail is ……………
Answer:
keratin.

7. The protein present in blood is …………..
Answer:
Haemoglobin.

8. ………….. has important role in providing immunity.
Answer:
Protein.

9. ………….. help in coagulation of blood oozing out continuously from any wounded region.
Answer:
Plasma proteins.

10. ………….. reduces heat emission from human body.
Answer:
Lipid.

11. Vitamins A D E and K are …………..
Answer:
Fat-soluble.

12. B-complex and C vitamins are ………….. vitamins.
Answer:
water-soluble.

13. Vitamin ………….. helps to maintain the structure of eye skin bones and teeth.
Answer:
A

14. Vitamin …………… maintains the structure of bones and joints.
Answer:
D

15. Deficeincy of iron causes ……………
Answer:
Anaemia.

16. …………… controls mental abilities and mental growth.
Answer:
Iodine.

17. Deficiency of …………… causes increase in blood sugar level.
Answer:
zinc.

18. The …………… part of food comes out of the body as stool.
Answer:
undigested.

19. Excessive water loss from the body causes ……………
Answer:
dehydration.

20. Deficiency of proteins lipids and carbohydrates in the diet casues …………..
Answer:
Marasmus.

21. Protein malnutrition results in a disease called …………..
Answer:
Kwashiorkar.

22. The kitchen of plant is …………..
Answer:
leaf.

State whether True or False : (1 mark for each question)

1. High blood pressure is related with iodine.
Answer:
false

2. Iodine controls mental abilities and mental growth.
Answer:
true

3. Sodium maintains water level in body.
Answer:
true

4. Source of iodine is vegetables.
Answer:
false

5. Iron helps in transporting oxygen in tissues.
Answer:
true

6. Plant source of lipid is fish oil..
Answer:
false

7. Keratin is present in hair and nail.
Answer:
true

8. Collagen is present in tendon and ligament.
Answer:
true

9. Protein is the main food component of ground nut butter coconut.
Answer:
false

10. Deficiency of vitamin causes ulcer at the corner of lips.
Answer:
true

11. Due tr deficiency of iodine symptom of high blood pressure is seen.
Answer:
false

12. For deficiency of vitamin A.one can not read blackboard from the last bench.
Answer:
true

13. Processed foods are richest in nutritional value.
Answer:
false

14. The foods obtained directly from mature are called natural foods.
Answer:
true

15. About 75% of earth’s surface is covered by water.
Answer:
true

Match the column A with column B

Column A	Column B
a) Aquatic plants absorb water	i) 60% water by mass
b) High fever occurs in	ii) is the cause of blindness
c) Human body has	iii) which can not be digested
d) Natural foods are richest	iv) from plants or animals or from water
e) Deficiency of Vitamin A	v) with their whole body
f) We get phytochemicals	vi) Malaria or Pneumonia
g) Stool has fibres	vii)root and other parts
h) Plant absorb water through	viii) in nutritional value
i) Deficiency of iodine	ix) from tomato                        ‘
j) Animals get minerals              .	x) causes goitre

Answer:
a) Aquatic plants absorb water with their whole body.
b) High fever occurs in Malaria or Pneumonia.
c) Human body has 60% water by mass.
d) Natural foods are richest in nutritional value.
e) Deficiency of Vitamin A is the cause of blindness.
f) We get phytochemicals from tomato.
g) Stool has fibres which can not be digested.
h) Plant absorb water through root and other parts.
i) Deficiency of iodine causes goitre.
j) Animals get minerals from plants or animals or from water.

Very Short Questions & Answers : (1 mark for each question)

Question 1.
What is needed to do daily work?
Answer:
Energy is needed to do daily work.

Question 2.
What is the source of energy in our body?
Answer:
Healthy and balanced diet is the source of energy in our body.

Question 3.
Which is ‘energy giving food’?
Answer:
Carbohydrates are energy giving food.

Question 4.
Which is ‘body building food’?
Answer:
Protein is body building food’.

Question 5.
What are protective foods?
Answer:
Vitamins and minerals are protective foods.

Question 6.
Name some plant sources which supply carbohydrate.
Answer:
Rice, wheat, potato, beet, pulses etc. are some sources which supply carbohydrate

Question 7.
Name some animal sources which supply carbohydrate?
Answer:
Honey, milk, meat, liver etc. are some animal sources which supply carbohydrate.

Question 8.
Which disease occurs due to unavailability of glucose in cells?
Answer:
Diabetes Mellitus occurs due to unavailability of glucose in cells.

Question 9.
What are the functions of muscles of our hands?
Answer:
Muscles of hand help to lift, push, pull things.

Question 10.
What are the functions of muscles of our legs?
Answer:
Muscles of leg help in walking, running, climbing jumping etc.

Question 11.
What is the function of Heart?
Answer:
Circulation of blood in our body.

Question 12.
What is the function of Lungs?
Answer:
It helps in respiration.

Question 13.
What is the function of Intestine?
Answer:
Digestion of food is the function of Intestine.

Question 14.
Name the protein present in hair and nail?
Answer:
Keratin is present in hair and nail.

Question 15.
Name the proteins present in muscle?
Answer:
Actin, Myosin.

Question 16.
Name the protein present in Red Blood Corpuscle?
Answer:
Haemoglobin.

Question 17.
Which proteins are in blood plasma?
Answer:
Globulin. Fibrinogen.

Question 18.
Collagen protein is present in which body parts?
Answer:
Bone. Tendon, Ligament.

Question 19.
Nans some plant sources which supply protein.
Answer:
Pea, kindney bean, seeds of jackfruit, millet, corn, garlic, clove, turmeric etc.

Question 20.
Name some animal sources which supply protein.
Answer:
Ghana, Paneer, Crab, milk, meat, fish, eggs etc.

Question 21.
Name some plant sources of lipid.
Answer:
Coconut, jackfruit, vegetable cooking oil, whole wheat grain etc.

Question 22.
Name some animal sources of lipid.
Answer:
Fish oil, milk, curd, meat, ghee, butter, egg yolk, meat, cheese etc.

Question 23.
Beri-Beri causes due to lack of which vitamin?
Answer:
Vitamin B.

Question 24.
Which vitamin deficiency disease was common in Europe nearly 500 years ago?
Answer:
Scurvy.

Question 25.
Which vitamin deficiency casues scurvy?
Answer:
Vitamin C.

Question 26.
Which vitamin helps in blood clotting?
Answer:
Vitamin K.

Question 27.
Which plant sources supply vitamins?
Answer:
Ripe mango, pumpkin, fig, tomato, spinach, cabbage and other green leafy vegetables.

Question 28.
Which animal sources supply vitamins?
Answer:
Meat, ghee, eggs, milk, fish, etc.

Question 29.
Name some sources of vitamin B complex.
Answer:
Cereals, cabbage, leaves of raddish, small fishes, chili, milk etc,

Question 30.
Name some essential minerals which our body requires.
Answer:
Iron, Calcium, Magnesium, Sodium, Iodine, Zinc etc.

Question 31.
Which parts of the plant produce food?
Answer:
Food is produced in leaves and other green parts.

Question 32.
What is the right amount of water that one drink daily?
Answer:
A healthy adult shout eat 50 ml/kg body weight to meet the daily requirement.

Short Questions & Answers : (2 marks for each question)

Question 1.
What is food? Why is food essential?
Answer:
The source of our energy and disease resistant component is food.
All living beings need energy to remain alive and active. The food we eat provides us with energy as well as those things that our body needs to stay alive and healthy.

Question 2.
What are the main components of food?
Answer:
The main components of food are –

• Carbohydrate
• Protein
• Lipid
• Vitamin
• Water
• Mineral
• Food fibre
• Phytochemical.

Question 3.
Define macronutrients and micronutrients.
Answer:
Carbohydrates, fats and proteins make up to bulk of our food. They are called macronutrients.
Vitamins and minerals though crucial for health, are needed in small quantities. They are called micronutrients.

Question 4.
Why Food fibres and water are also important components of our food?
Answer:
Food fibres from the roughage part of our food. They help in the movement of bowel in the intestine. Water helps our body to absorb nutrients from the food. It also helps in removing wastes from the body.

Question 5.
Mianly how many types of carbohydrate are there in our food?
Answer:
Carbohydrate which we get from our food to keep us strong is mainly of two types— glucose and starch.

Question 6.
How is energy produced in our body?
Answer:
Energy is produced in the cells of the healthy body by breakdown of glucose. That energy is required for different works.

Question 7.
‘Sometimes intake of milk causes problem’, — What is the reason behind it?
Answer:
Some children or aged persons suffer from different problem after intake of milk or milk products. Indigestion of leactose, a milk carbohydrates, leads to this type of problem.

Question 8.
What leads to obesity? In which body parts lipid is stored in huge amount in an obese person?
Answer:
Eating more of energy-rich food than required by the body causes I ipid deposition in the body and leads to abesity. Lipid containing body parts are neek, upper arm, chest, abdomen and thigh, in an obese person.

Question 9.
How is lipid important? What problem will arise if lipid is stored more than necessary?
Answer:
Lipid acts as sources of energy in the human body and protects the body from external injury. It also reduces heat emission from human body. If more than necessary lipid is stored, the condition can create different problems in heart, blood vessel and liver.

Question 10.
How many types of vitamins are there?
Answer:
Vitamins are of two types—

• Fat-soluble vitamin—A, D, E and K.
• Water-soluble vitamin—B complex and C.

Question 11.
Name some natural pigments which are present in food from plant sources. How are they helpful to us?
Answer: Some coloured pigments present in plant sources are caroteinoids, flavonoids. They stop fast ageing of human body, keeps healthy functioning of heart, strengthen bones. They also check cancer.

Question 12.
What is balanced diet?
Answer:
The diet which contains all the essential nutrients in just the right proportion is called a balanced diet. It varies from person to person depending upon sex. age, group of profession.

Question 13.
What are the symptoms of malnutrition in the child?
Answer:

• Decay of bone in body.
• Muscle is distinct from outside.
• Skin is wrinkled here and there.
• Hands and legs are thin.

Question 14.
Below write the names of different dificiency diseases.
1. Iron dificiency = —
2. Iodine deficiency = —
3. Vitamin D deficiency = —
4. Vitamin B complex deficiency = —
5. Vitamin A dificiency = —
6. Deficiency of protein and energy = —
Answer:
1. Anaemia
2. Goitre, mental retardation, squint
3. Ricket
4. Beriberi
5. Blindness
6. Marusmus, Kwashiorkar.

Question 15.
Why artificial food should not be taken in huge quentity?
Answer:
Artificial food is highly priced by the nutrient level in near by nil. Over consumption of these foods leads to problem of heart, liver, kidney, bones or brain.

Question 16.
What are the symptoms of low blood pressure?
Answer:
Hyponatremia ossures when sodium levels in the blood are too low. Symptoms include lethargy, confusion, and fatigue.

Long Questions & Answers : (3 marks for each question)

Question 1.
Why the diseases Mamasmus and Kwashiorkar occur?
Answer:
The disease caused by malnutrition is called Marusmus. Deficiency of protein and energy in diet lead to this disease. This is predominant in children below one year. Kwashiorkar disease develops in children of 1-4 years old due to deficiency of protein. Children . suffering from Kwashiorkar show stunted growth, large potlike belly, mental retardation swollen face and dark skin.

Question 2.
What can be the reason of obesity? What are the effects of obesity?
Answer:
Obesity occurs due to excessive intake of junk food like pizzas, potato wafers, noodles, icecream and soft drinks which contain excessive lipid. Viewing of TV instead of playing outdoor games, is another cause of obesity. Obese persons are prone to heart disease and high blood pressure (hypertension), ft leads to arthritis, diabetes and anaemia. Obesity also causes discomfort and breathlessness.

Question 3.
When malnutrition occurs?
Answer:
The chance of malnutrition increases if deficiency of energy producing food components are found in diet. Energy producing food components are carbohydrate, protein and lipid. Deficiencv of other food components (vitamin and mineral) also lead to many problems. Worms can be a reason for malnutrition.

Question 4.
Discuss role of water and light in production of food in plants.
Answer:
Plant absorbs water through root and other parts, sends the absorbed water to leaves. Plant absorbs a small amount of light energy from sunlight. Plants begin the process Photosynthesis with the help of light energy and green pigment chlorophyll. Food is produced in leaves and other green parts by water, sunlight and carbon dioxide absorbed from air.

Question 5.
Describe the importance of water in our body.
Answer:
Water is needed for the following functions :

• It maintains our body temperature.
• It is needed in the excretion of wastes.
• It acts as a medium for biochemical reactions in our body.
• It helps in the transportation of nutrients within the body.
• It is an essential part of digestive juices and blood.

Question 6.
What is fibre? How is food fibre helpful?
Answer:
Fibre is a type of Carbohydrate of the nature of cellulose or protein. These may or may not be dissolved in water. The food fibres are formed of cellulose. Since we cannot digest cellulose, human body cannot yield energy from food fibres, it also does not provide us any nutrients.

They simply add bulk to our food and help to get rid of undigested food. Therefore, food fibre help in proper digestion of food as well as in easy and regular movement of bowel. This prevents constipation, colon cancer, obesity high blood pressure and reduces acidity in the stomach.

Question 7.
What will happen if glucose does not enter into cell from blood?
Answer:
Glucose then circulates through blood till it excretes out from the body through kidney. Different organs (heart, kidney, eye, leg) malfunction due to unavailability of glucose in cells. This condition is termed as Diabetes Mellitus. This disease is very common in India. Proper diet and regular exercise can help to prevent this disease.

Question 8.
Why are minerals necessary? Mention some of its function.
Answer:
Minerals are necessary for proper growth of body and to maintain good health, like vitamins, minerals does not supply energy to our body. Some functions are —

• Calcium — maintains muscle contraction, helps in blood coagulation.
• Sodium — maintains water level in body.
• Iron — helps in transport of oxygen, needed for the formation of red blood cells.
• Iodine — controls mental abilities and mental growth.
• Zinc — maintains brain functioning and blood sugar level.
• Calcium, Phosphorus, Magnesium — develop bones and teeth.

Question 9.
Name some minerals necessary for our body. How do plants and animals obtain these minerals?
Answer:
Some minerals necessary for our body are — Iron, Calcium, Magnesium, Sodium, Potassium, Zinc etc.
The minerals are obtained from living organisms as well as non-living compounds.

• Plants collect minerals from soil or ground water under soil.
• Animals get minerals from plant foods, animal foods or water.

Question 10.
What would happen if body looses excessive water? What precautions should be taken then?
Answer:
Excessive water loss from the body causes dehydration. Due to dehydration blood becomes thicker, causing severe pain and cramps. In order to make up the loss of water and minerals from the body, we should drink a solution prepared by adding one teaspoonful of sugar and a pinch of salt to 200 ml of water. This solution is called Oral Rehydration Solution (ORS).

Question 11.
What is starch? How is glucose important to our body?
Answer:
Starch is a complex carbohydrate. In the process of digestion, starch, is broken down into the smallest units (Glucose). This glucose is transported to peripheral regions through blood. Here the absorbed oxygen helps in production of energy from glucose in body. This energy helps in different performances.

Question 12.
Describe the importance of protein in our body. What will happen if there is excess protein in our body?
Answer:
Different kinds of proteins play important roles in producing energy, formation of tissue or parts of body, healing wounds, transport of respiratory gases, contraction of muscles. Protein has important role in providing immunity. Plasma proteins help in coagulation of blood oozing out continuously from any wounded region. Excess protein in body can lead to arthritis, renal stone and other problems.

Question 13.
Which vitamins (A, D, E, K) are needed in the following cases?
Answer:

Problems	Vitamin
1. Short sight at night	A
2. Curved bones and curved vertebral column	D
3. blood doesn’t easily coagulate in wounded areas	K
4. Damage of red blood cells, heart, brain activity hampered	E

Question 14.
Symptoms are given write down the names of water-soluble vitamin necessary.
Answer:

Symptoms	Vitamin
1. Cracked lips	B-complex
2. Nails and lower part of eye becomes pale	B-complex
3. Loosening and falling of tooth	C
4. Nervous disorder	B-complex
5. Loose motion, Demensia	B-complex

 

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 11 Plant Kingdom and the Environment Around Us offer valuable context and analysis.

WBBSE Class 8 Science Chapter 11 Question Answer – Plant Kingdom and the Environment Around Us

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
Every year each water hyacinth produces seeds —
i) less than five hundred
ii) less than thousand
iii) more than thousand
iv) less than hundred
Answer:
iii) more than thousand

Question 2.
Now-a-days bamboo fabrics are used for making —
i) clothes
ii) papers
iii) ropes
iv) medicines
Answer:
i) clothes

Question 3.
Resin derived from sal tree are used for making —
i) shoe polish
ii) gum
iii) chocolates
iv) spirit
Answer:
iv) spirit

Question 4.
Now laws are framed to protect —
i) Sal plant CL
ii) Sundari plant
iii) Bamboo plant
iv) water Hyacinth
Answer:
ii) Sundari plant

Question 5.
We get cinnamon from —
i) bark of tree
ii) fruits of tree
iii) flower of tree
iv) seeds of tree
Answer:
i) bark of tree

Question 6.
Black peeper is used in —
i) nausea
ii) diarrhoea
iii) cold
iv) liver diseases
Answer:
iii) cold

Question 7.
Curcumin is found in —
i) Cinnamon
ii) ginger
iii) garlic
iv) turmeric
Answer:
iv) turmeric

Question 8.
Ginger is useful in —
i) gum problem
ii) stomach upset
iii) anemia
iv) pain in gum
Answer:
ii) stomach upset

Question 9.
A compound called Alicin is rerived from —
i) ginger
ii) cardamom
iii) garlic
iv) turmeric
Answer:
iii) garlic

State whether True or False : (1 mark for each question)

1. Bamboo is one of the lowest growing tree of the world.
2. Different bamboo-made utensils are used for the purpose of cooking.
3. Water hyacinth is a good source of biogas as it contains high amount of oxygen.
4. Sal is a type of coniferous tree.
5. The fruit of Sundri plant is egg-like but is slightly elongated.
6. Spices were used to preserve meat.
7. Ginger and Turmeric are fruits of plant.
8. Saffron is floral part of plant.
9. Cinnamon is prepared by drying leaf of the cinnamon tree.
10. Turmeric is also used to dye different foods and medicines.
Answer:
1) false
2) true
3) false
4) false
5) true
6) true
7) false
8) true
9) false
10) true.

Fill in the blanks : (1 mark for each question)

1. Plants are sources of ………….. as well as ………….. for animals also.
2. ………….. is one of the fastest growing tree of the world.
3. The major food of Gorillas of Africa is …………..
4. ………….. an importanit medicine is derived from inter mode of bamboo species namely
5. ………….. mosquitoes propagate in the densely grown water hyacinth plants.
6. ………….. derived from bank of Sal are used in leather industry.
7. Sundri trees grow in sweet water of saline areas of ……………
8. Apart from enhancing the taste of food spices are also used as ………….
9. Clove contains a chemical substance called ………….. which has anti-bacterial properties.
10. In different countries of the world almost …………. types of spices are cultivated.
11. Black pepper is a perenuial …………..
12. ………….. is responsible for the hot taste of black pepper.
13. Cinnamon is prepared by drying the ………….. of the cinnamon tree.
14. ………….. is a peremial herb.
15. A compound, called ………….. is found in turmeric.
16. Seeds of greater cardamom alleviates …………..
17. Each bulb of garle is termed as ………….. of garlic.
18. Garlic contains a compound called ……………
19. At present around species of medicinal plants are found in our country.
20. Juice of neem leaves is very useful for……………
21. Bael fruit contains ………….. and ………….., which is a panacea for constipation.
22. Emblica fruit contains huge amount of ……………
23. ………….. leaves are useful in bleeding haemorrhoids and wasp sting.
24. Mint sherbat is a useful digestive for ………….. troubles.
25. Extract of aloevera leaves is used to reduce ………….. and …………..
Answer:
1) shelter, food
2) Bamboo.
3) bamboo
4) Tabashir. Bambusa arundinacea.
5) Aedes
6) Tannin
7) Sunderban
8) preservative
9) Eugenol.
10) eighty
11) vine
12) Piperine
13) inner, bark
14) Turmeric
15) curcumin
16) nausea
17) grates
18) Alicin
19) 3500
20) diabetes
21) mucilage, pectin
22) Vitamin C
23) Cantharanthus
24) stomach
25) mental stress, tension.

Match the column A with column B.

Column A	Column B
a)  Neem oil is used for b)  Unripe bael increases c) Catharanthus leaf is a good nedicine d)  Extract of aloevera leaves is used e) Garlic is effective in f) Cardamom is used in preparing g) Turmeric has the ability h) Cinnamon has its own	i) for diabetes ii) various problem of heart iii) different sweet dishes iv) to kill bacteria v) sweet aroma and taste vi) pain in ear vii) appetite and digestive power viii) in constipation

a) Neem oil is used for pain in ear.
b) Unripe bael increases appetite and digestive power.
c) Catharanthus leaf is a good nedicine fordiabetes.
d) Extract of aloevera leaves is used in constipation.
e) Garlic is effective in various problem of heart.
f) Cardamom is used in preparing different sweet dishes.
g) Turmeric has the ability to kill bacteria.
h) Cinnamon has its own sweet aroma and taste.

Very Short Questions & Answers : (1 mark for each question)

Question 1.
Name one of the fastest growing tree of the world.
Answer:
Bamboo

Question 2.
How is the stem of bamboo?
Answer:
Stem are long pipe-like and with less branches.

Question 3.
What is the rate of growth in some species of bamboo plant?
Answer:
100 cm in each 24 hour.

Question 4.
Name some endangered animals whose cheif food is different part of bamboo.
Answer:
Giant panda of china, Red panda of Nepal and India and Lemur of Madagascar.

Question 5.
How hollow stems of bamboo are used in different places of South Africa.
Answer:
For warming soups and as pot for cooking rice.

Question 6.
For how many years water hyacinth live?
Answer:
For 24 years.

Question 7.
Name some countries where the stems of water hyacinth arc used for the purpose of embroidery and garment industries.
Answer:
Philippines. Thailand and Vietnam.

Question 8.
How many years Sal take to mature.
Answer:
25 to 30 years.

Question 9.
Name a plant in which stilt root is present.
Answer:
Sundri

Question 10.
How the fruit of Sundri plant look like?
Answer:
The fruit of Sundri plant is egg like but is slightly elongated.

Question 11.
What is the colour of Sundri plant fruit?
Answer:
Brownish.

Question 12.
Name a centre for rearing and conserving Sundri plant.
Answer:
Jharkhali.

Question 13.
Name some places where Indian spices, perfumes and fine clothing materials travelled in past?
Answer:
Mesopotemia, Arabia and Egypt.

Question 14.
What chemical substance present in clove has anti-bacterial properties?
Answer:
Clove contains a chemical substance Eugenol, which has anti-bacterial properties.

Question 15.
Name some spices which arc seeds of plant.
Answer:
Ajowan, Fennel, Coriander, Mustard, Poppy seeds. Aniseed.

Question 16.
Name a plant whose seed is used as spies.
Answer:
Clove.

Question 17.
Name some rhizomes used as spices.
Answer:
Ginger, Turmeric.

Question 18.
Which part of plant is Asafoctida spice?
Answer:
Exudates.

Question 19.
Name some leaves used as spices.
Answer:
Cassia leaf (Tejpata), Mint.

Question 20.
Name some fruits of plant used as spices.
Answer:
Black pepper, Cardamom, Chillies.

Question 21.
Name a kernel of plant used as spices.
Answer:
Nutmeg.

Question 22.
What is the colour of Black pepper when it is unripe and after ripening?
Answer:
Unripe fruits of Black pepper are green and become reddish in colour after ripening.

Question 23.
When Black pepper turns black?
Answer:
The ripe fruit becomes black when they are dry.

Question 24.
What is the taste of Black pepper?
Answer:
The taste of Black pepper is hot.

Question 25.
What is responsible for the hot taste of Black pepper?
Answer:
Piperine is responsible for the hot taste of Black pepper.

Question 26.
How is cinnamon prepared?
Answer:
Cinnamon is prepared by drying the inner bark of the cinnamon tree.

Question 27.
How many types of Cinnamon are there?
Answer:
Two types – thick bark and thin bark.

Question 28.
What compound is found in turmeric?
Answer:
Curcumin compound.

Question 29.
How the presence of Curcumin compound in turmeric is helpful?
Answer:
Due to its presence, turmeric has the ability to kill bacteria, viruses and fungi.

Question 30.
Why is Turmeric effective in anemia?
Answer:
Turmeric is effective in anemia due to the presence of good amount of iron in turmeric.

Question .
How many types of Cardamom arc there?
Answer:
Two types -greater cardamom and lesser cardamom.

Question 32.
What is the colour of dried greater cardamom and lesser cardamom?
Answer:
Dry Greater cardamom is coppery in colour and dry lesser cardamom is light brown in colour.

Question 33.
Why fully ripe fruits of cardamom not selected for artificial drying?
Answer:
Suice ripe fruits may burst while being dried.

Question 34.
Generally how Garam Masala is prepared?
Answer:
Garam Masala is prepared by mixing clove, cardamom, cinnamon, black pepper, mace and nutmeg.

Question 35.
What arc grates of garlic?
Answer:
A bulle of garlic consists of 6-30 small bulb-like parts. These are termed as grates of garlic.

Question 36.
Name the compound present in Garlic?
Answer:
Alicin compound is present is Garlic.

Question 37.
Which veda describes the medicinal properties of different plants?
Answer:
Atharva Veda.

Question 38.
According to WHO what percent of population depend on traditional medicines for primary treatment?
Answer:
80% population.

Question 39.
How many species of medicinal plant is found only in Asia?
Answer:
8,500 species.

Question 40.
At present how many types of medicinal plant is present in our country?
Answer:
3,500 species.

Question 41.
How is Bael fruit helpful for constipation?
Answer:
Bael fruit contains mucilage and pectin, which is a pancea for constipation.

Question 42.
What is Triphala?
Answer:
Triphala is kind of ayurvedic medicine.

Question 43.
How many fruits are present in Triphala?
Answer:
Three fruits – Emblica, Chebulic myrobalan (Haritaki) and Belleric myrobalan (Bahera) (without seed).

Question 44.
Name the alkaloid present in the root of Catharanthus (Nayantara) helpful in removing obstacles in blood circulation in brain?
Answer:
Raubasine.

Question 45.
Name two alkaloids present in Catharanthus helpful in treatment of Cancer?
Answer:
Vincristine mid Vinblastine.

Question 46.
What aioevera leaves contain?
Answer:
Aioevera leaves contains vitamins, minerals, amino acid and fatty acid.

Short Questions & Answers : (2 marks for each question)

Question 1.
In middle ages what was the utility of spices?
Answer:

• There was no refrigerator in that age. So spices were used to preserve meat,
• Spices enhanced the taste of food.

Question 2.
Mention two medicinal properties of Bael fruit.
Answer:

• Bael fruit contains mucilage and pectin, which is a panacea for constipation,
• Juice of bael fruit takes care of intestine of diarrhoea patients.

Question 3.
How do we get spices?
Answer:
We get spices from different parts of plants. Such as — cinnamon from bark of tree, clove from buds, black peeper, cardamom from fruits, tejpata mint from leaves, ajowan aniseed fennel from seeds, nutmeg from kernel.

Question 4.
Write two medicinal value of ginger.
Answer:
Ginger is useful in stomach upset, heartburn or problems related to gas, cough and asthma. Taking pieces of ginger with salt before eating specially in monsoon or winter season, increases appetite.

Question 5.
How black peeper looks like?
Answer:
Its unripe fruits are green and become reddish in colour after ripening. The ripe fruit becomes black when they are dry.

Question 6.
What is the medicinal value of bamboo?
Answer:
Tabashir, an important medicine for asthma, cold and cough and many infestious disease <s made from silicon dioxide and silicic acid. These are derived from intermode of bamboo spscies namely Bambusa arundinacea.

Question 7.
Can water hyacinth be used in industries?
Answer:
The items of witter hyacinth are used for the purpose of embroidery and as a source of fibres for garnish dustries in many countries of the world. Fibres of it are being used in paper manufacturing.

Question 8.
Mention two uses of emblica.
Answer:

• Emblica works well in nausea and constipstion.
• Emblica is effective in prevention of anemia and cancer.

Long Questions & Answers : (3 marks for each question)

Question 1.
How are plants useful to us?
Answer:

• Animals utilise oxygen, exhaated by plants, for their respiration.
• Plants serve as a source of shelter as well as food for animals.
• Plants reduce the extent of pollution by absorbing pollutants.
• Plants impart different roles for controlling temperature, rainfall, wind velocity.
• Different parts of plants are being used as raw materials for different industries.
• Parts of some plants or even the whole plant body are used as manure.

Question 2.
Mention any four uses of bamboo plant?
Answer:

• The young stem, basal part of stem and leaves of bamboo plants are chief foods of many critically endangered animals of world.
• Different delicious dishes are being prepared at different countries of Asia using soft young stems coming out from the base of bamboo.
• In India bamboo is used for manufacturing paper, baskets, handle of umbrella, flower vase, tray, flutes, different types of toys and for interior decoration of rooms.
• Tabashir, an important medicine for asthma, cold and cough and many infectious diseases is made from silicon dioxide and silisic acid derived from internode of bamboo species namely Bambusa arundinacea.

Question 3.
Write three uses of water Hyacinth.
Answer:

• Water hyacinth is a good source of biogas as it contains high amount of nitrogen.
• Abater hyacinth is a tolerant species of plant. It can purify polluted dirty water by absorbing
  heavy metals like Cadmium, Chromium, Cobalt, Nickel, Lead and Mercury. As a result water become pollutant free and become suitable for us for different purposes.
• The demand for water hyacinth as fodder is increasing day by day as it contains high amount of protein or nitrogen.

Question 4.
Write three different uses of Sal plant.
Answer:

• Sal tree are of greater use in making poles, furniture, frame of doors and windows, floor of boats, jetty of the ship and foot bridge over rivers.
• From the gum of Sal tree red resius with fragrance are derived. These resins are used for

Question 5.
For what purposes we use spices?
Answer:

• To bring taste to bland food items.
• Use it as preservative (in pickles, Chutneys etc).
• Helps in digestion by increasing salivation.
• Helps keeping the mouth-cavity germ-free.

Question 6.
Write two uses of Black pepper and Cinnamon.
Answer:
Uses of Black pepper —

• Black pepper is used in cough, toothache, bleeding from the gum pain in gum and indigestion.
• Black pepper is used as preservative for meat and other perishable food items.

Uses of Cinnamon —

• Cinnamon is used in small pieces or in powdered form in cooking.
• In diarrhoea, nausea, vomitting and for cold, cinnamon is useful.

Question 7.
Write three medicinal uses of turmeric.
Answer:

• Turmeric helps in keeping the liver health
• Turmeric is effective in anemia due to the presence of good amount of iron in turmeric.
• Due to the presence of Curewntn compound in turmeric, it has the ability to kill bacteria, viruses fungi.

Question 8.
How is Cardamom useful to us?
Answer:

• Cardamom has its use in stomach related problems.
• Cardamom is taken with bital leaf and also as a mouth freshner.
• Greater cardamom strengthens gum.
• Seeds of greater cardamom alleviates nausea.

Question 9.
Mention some uses of Garlic.
Answer:

• Alicin compound in Garlic has anitmicrobial properties.
• Garlic helps to alleviate gas related problem.
• Garlic helps in food digestion, by stimulating the stomach.
• it is effective in various problems of heart and blood vessels.

Question 10.
How the different parts of neein tree like — Steam, leaves, root etc are important to us?
Answer:

• Juice of neem leaves is very useful for diabetes,
• Neem seed has its use in viral epidemic and arthritis.
• Neem oil extracted from leaves and stem is used for pain in ear, as well as gum and toothache. It is also used to maintain the health of hair, to increase the working capacity of the liver and as a blood cleanser.
• The bitter tonic prepard from the bark of root and stem is useful in breaking the periodic sequence of fevers (like malaria). It has its use also in skin diseases.

Question 11.
Write medicinal properties of Embiica fruit.
Answer:
Embiica fruit contains huge amount of Vitamin C. Embiica fruit is useful in the swelling of gum. Dry empirical fruit is capable to stop stomach upset, hemorrhage and dysentery. Embiica works well in nausea and constipation. It is effective in prevention of anemia and cancer.

Question 12.
What is Triphala? How is it useful?
Answer:
Triphala is a kind of ayurvedic medicine. Triphala contains three fruits Embiica (Amtaki), Chebulic myrobalan (Haritaki) and Belleric myrobalan (Bahera) (without seed). Powdered triphala is used as purgative which helps to clean the alimentary canei. Triphala is used as a blood-cleanser. Triphala contains Vitamin C. for this reason triphala is used as supplementary food.

Question 13.
How are alkaloids present in Catharanthus useful?
Answer:
An alkaloid called Raubasine is present is the root of this plant and it helps to remove obstacles in blood circulation in the brain. Vineristine and Vinblastine two alkaloids present in Catharanthus are presently used to treat blood cancer and certain other types of cancer. These two aikoioids are also effective in restraining tumour growth.

Question 14.
Write two medicinal properties of Mint (Pudina) and Aloevera.
Answer:
Mint (Pudina) —

• Mint is useful in flatulence, indigestion, loose stool of infants and bad breath.
• Mint is useful in cough, loss of appetite and inflammation of stomach.

Aloevera —

• Extract of aloevera leaves is used to reduce excess of acidity, tendency of blood to become thick, stress due to pollution and inflammation of bone joints.
• Extract of aloevera is used in fever to reduce temperature as it contains an anti-pyretic component.

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 2.4 Chemical Effects of Electricity Reaction offer valuable context and analysis.

WBBSE Class 8 Science Chapter 2.4 Question Answer – Chemical Effects of Electricity

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
Which of the following is non-eiectrolyte?
i) pure water square
ii) solution of glucose and water square
iii) liquid ammonia square
iv) all of tise above
Answer:
iv) all of the above

Question 2.
Which of the following is electrolyte?
i) soluton of sugar and water
ii) graphite
iii) water solution of H₂ SO₄
iv) water solution of glucose
Answer:
iii) water solution of H₂ SO₄

Question 3.
During zinc plating in anode is given-
i) iron item
ii) copper item
iii) graphite rod
iv) zinc rod square
Answer:
iv) zinc rod

Question 4.
During electrolysis of water gas produced in anode is-
i) oxygen
ii) hydrogen
iii) chlorine
iv) nitrogen
Answer:
i) oxygen

Question 5.
Plating of zinc is done to-
i) to increase beauty
ii) to prevent rusting
iii) none of the above
iv) both of the above
Answer:
iv) both of the above

Question 6.
Plating with zine is called-
i) Seradisation
ii) Galvanisation
iii) Oxidation
iv) Reduction is
Ans:
ii) Galvanisation

Question 7.
Metal used for coating on iron pipe-
i) zinc square
ii) silver
iii) nickel
iv) chromium
Answer:
iii) nickel

Question 8.
Electrolysis is used for-
i) metal extraction
ii) purification of metals
iii) electroplating
iv) All the above
Answer:
iv) All the above

State whether True or False : (1 mark for each question)

1. After a long use the handle of a bicycle lose their glaze.
2. To remove the impurities, the impure copper is purified by electroplating method.
3. In electrolysis insulated electrical wires are required for sonnections.
4. Substances like butter, ghee are not soluble in water.
5. The electrode sonnected with the positive end of battery is called cathode.
6. Disilled water mixed with salt is a bad conductor of electricity.
7. Examples of electrolytes are acid, alkali solution.
8. Elcctrolysis of fused NaCl produces sodium metal.
Answer:
1. true
2. false
3. true
4. true
5. false
6. false
7. true
8. true

Fill in the blanks : (1 mark for each question)

1. Conduction of electricity through a metai means movement of _______.
2. CuSO₄ is a ______ electrolyte.
3. The compounds which do not prodace ions are calied _____.
4. The hope of _____ is taken to give the metallic coating on an object of another metal.
5. Rusting of iron occurs in contact with ____ and moisture of air.
6. Parts of a bicycle or a car or a bran tap are coated with ____.
7. To protect iron tools or utensils from rusting a thin coating of ____ is given on them.
8. Nickel plated substances are attracted by _______.
9. Impure copper is purified by _______ method.
10. Some electrolytes remain completely _______ in solution.
11. An LED can glow even at a low _______.
12. During electroplating the substance on which plating to be done is taken as _______.
Answer:
1. electrons
2. strong
3. non-clectrolytes
4. electrolysis
5. oxygen
6. chromium
7. nickel
8. magnet
9. electrolytic
10. dissociated
11. current
12. cathode

Match the following : (1 mark for each question)

a) Match the column A with column B.

Column A	Column B
a) In elect: olysis of water get	i) are essential for our body
b) coating of zinc is given	ii) impure metal is taken as anode
c) Salt mixed water	iii) is a strong electrolyte
(d) NaCl	iv) is a bad conductor of electricity
e) Solution of water and glucose is	v) hydrogen and oxygen
f) At the time of electro- plating	vi) is a good conductor of electricity
g) Minerals present in drinking water	vii) in the process of electrolysis

Answer:
a) In eletrolysis of water we get hydrogen and oxygen.
b) Coating of zinc is given in the process of electrolysis.
c) Salt mixed water is good conductor of electricity.
d) NaCl is a strong electrolyte.
e) Solution of water and glucose is a bad conductor of electricity.
f) At the time of electroplating impure metal is taken as anode.
g) Minerals present in drinking water are essential for our body.

Very Short Questions & Answers : (1 mark for each question)

Question 1.
Name a non-metal conductor.
Answer:
Graphite is a non-metal conductor.

Question 2.
Give an example of electrolyte.
Answer:
NaCl is an electrolyte.

Question 3.
Name a non-electrolyte.
Answer:
Sugar is a non-electrolyte.

Question 4.
Name a substance which is electrolyte even in solid state.
Answer:
Sodium.

Question 5.
To give a coatng of copper on a substance what is given as electrolyte solution?
Answer:
Water solution of copper’sulphate

Question 6.
Split (NH₄)₂ SO₄ in ions.
Answer:
(NH₄)₂ SO₄ = 2+

Short Questions & Answers : (2 marks for each question)

Question 1.
What are electrolytes? Give example.
Answer:
The compounds which are able to conduct electricity in a fused state or in a solution, are called electrolytes. Examples of electrolyies are acid or aikyle soluton, aqueous solution of a salt, fused NaCl etc.

Question 2.
What is electroplating?
Answer:
Electroplating is the process by which electric current is use to deposit one metal on the surface of another metal.

Question 3.
During electroplating which is taken as cathode and anode?
Answer:
During electroplating the substance on vhich plating is to be done is taken as cathode. The metal with which it is to be plated is taken as anode.

Question 4.
What is galvanized iron?
Answer:
Rusting of iron occurs in contact with oxygen and moisture of air. So another metal, zinc is coated over iron. It is called zinc-plated or galvanized iron.

Question 5.
How can you differ between stainless steel and nickel-coated iron?
Answer:
Nickel plated iron is attracted by a magnet very strongly, whereas stainless steel is not strongly attracted by a magnet.

Question 6.
Why wax, butter, ghee etc are non-clectrolytes?
Answer:
To be an electrolyte. a substance must produco ions in a fused state or in solution. None of these compounds produce ions. so these are not electrolytes.

Long Questions & Answers : (3 marks for each question)

Question 1.
Name the ions produced by potassium hydroxide, sulphuric acid and potassium nitrate in an aqueous solution.
Answer:
potassium hydroxide arrow K and OH
Sulphuric acid arrow H^– and
Potassium nitrate arrow K^– and

Question 2.
What is eiectrolysis?
Answer:
When chemical change of a substance occurs upon passage of electricity through a fused state or a solution, it is called electrolysis. Electrolysis is a redox reaction. Reduction occurs at cathode, the electrode connected to the negative terminal of the battery. Oxidation occurs at anode, the electrode connected to the positive terminal of the battery.

Question 3.
Why some acid or alkali is added with pure water in an experiment?
Answer:
Actually, the number of ions in pure water is so low, that it is not a good conductor of electrcity. So the number of ions in water must be increased. For this purpose some alkali ( NaOH or KOH ) or some acid (H₂ SO₄) is to be added to water. As they are strong electrolytes, the number of ions in the solution increases. Then it becomes possible to carry out electrolysis.

Question 4.
What are strong and weak electrolytes?
Answer:
Some electrolytes remain completely dissociated in solution. These are called strong electrolytes. e.g NaCl. KOH, H₂ SO₄, CuSO₄ etc.
There are some electrolytes that remain ionised in solution only to a very small extent. These are called weak electrolytes. e.g acetic acid.

Question 5.
Give three important uses of electrolysis.
Answer:
i) Metal Extraction : Some metals are separated from their compounds by electrolysis. Some of these are sodium, potassium and calcium.
ii) Purification of metals: The metal primarily obstained from copper are is impure. To remove the impurities, the impure copper is purified by electrolytic method.
iii) Electroplating : Articles made of iron or steel are electroplated with nickel or chromium through electrolysis to prevent them from rusting.

Detailed explanations in West Bengal Board Class 9 Physical Science Book Solutions Chapter 2 Force and Motion offer valuable context and analysis.

WBBSE Class 9 Physical Science Chapter 2 Question Answer – Force and Motion

Very short answer-type questions

Question 1.
Of mass and weight of a body, which is more fundamental ?
Answer:
Mass is more fundamental than weight.

Question 2.
What is the ultimate form of all energies ?
Answer:
Heat energy.

Question 3.
In which part of the earth the weight of a body is maximum ?
Answer:
The weight of a body is maximum at the two poles of the earth.

Question 4.
Which type of balance is used to measure the weight of a body ?
Answer:
Spring balance.

Question 5.
What is the ultimate source of all energies ?
Answer:
The sun.

Question 6.
In an electric cell which type of energy changes to which other ?
Answer:
Chemical energy to electric energy.

Question 7.
What is the principle of solar cooker?
Answer:
In a solar cooker, heat energy of the sun is trapped in a box producing sufficient heat.

Question 8.
Why does wind possess energy ?
Answer:
Wind possesses energy due to speed of air particles.

Question 9.
How is tidal energy explored?
Answer:
Water stored at a higher level during high tide possesses potential energy that converts to kinetic energy when the water comes down during low tide.

Question 10.
What will be observed when the mass of a body is measured with a common balance on the surface of the earth and at the top of a mountain ?
Answer:
Mass of the body will be same at both the places.

Question 11.
When a body is taken to a high altitude from the earth, what changes of mass and weight of the body are observed ?
Answer:
Mass remains same, weight decreases.

Question 12.
Where does a body weigh more, at the equator or at the poles of the Earth ?
Answer:
A body weighs more at the poles than at the equator, for, the poles are nearer to the centre of the earth than the equator.

Question 13.
In what type of balance is mass of a body measured ?
Answer:
Mass of a body is measured in common balance.

Question 14.
Write down the relation between mass and weight.
Answer:
Weight of a body = mass of the body × acceleration due to gravity.

Question 15.
Why does the weight of a body change at different places ?
Answer:
Weight of a body given by the equation, w=m g, changes due to variation of ‘g’ at different places.

Question 16.
Does a spring balance show the same weight of a body at different places?
Answer:
No. Weight of a body changes at different places due to variation of ‘g’. So, a body weighed with a spring balance at different places show different weights.

Question 17.
Write down the names of non-conventional sources of energy.
Answer:
Some non-conventional sources of energy : (i) Solar energy (ii) wind energy (iii) Tidal energy.

Question 18.
Give an example of transformation of electrical energy to heat energy.
Answer:
In electric heater and electric iron, conversion of electrical energy into heat energy takes place.

Question 19.
Give an example of transformation of heat energy to electrical energy.
Answer:
Two different metal wires are joined at two ends. One end is kept in ice and the other end is heated. Electric current will flow through the wire. This is the conversion of heat energy into electrical energy.

Question 20.
Give an example of transformation of mechanical energy to electrical energy.
Answer:
In dynamo, rotation of a wire wheel in a magnetic field produces electric current. Hence mechanical energy of the wheel is converted into electrical energy.

Question 21.
Give an example of transformation of sound energy to electrical energy.
Answer:
In telephone and microphone, sound energy is converted into electrical energy.

Question 22.
Give an example of transformation of light energy to electrical energy.
Answer:
In photo-electric cell light produces electricity.

Question 23.
How is potential energy converted into kinetic energy ?
Answer:
When one object is kept at an elevated position, it is stationary there. Its total energy is potential energy. But when it is allowed to fall on the earth its potential energy is converted into kinetic energy.

Question 24.
Name an energy not derived from solar energy.
Answer:
Nuclear energy is not derived from solar energy.

Question 25.
Can energy be destroyed ?
Answer:
Energy can not be destroyed. It can only be transformed from one form to the other.

Question 26.
Is wood matter ?
Answer:
Wood is an example of matter as it exists in nature occupying some space.

Question 27.
Does mass of a body change with the change of place ?
Answer:
Mass of a body is its intrnsic property and it remains same everywhere.

Question 28.
What is the absolute unit of weight in SI system ?
Answer:
Newton.

Question 29.
What is the absolute unit of weight in CGS system ?
Answer:
Dyne.

Question 30.
What is the value of acceleration due to gravity (g) in SI system ?
Answer:
9.81 m / sec²

Question 31.
Give an example of transformation of kinetic energy to potential energy.
Answer:
When an object is thrown vertically upwards, its kinetic energy is converted into potential energy.

Question 32.
What will be the weight of a thing in artificial satellite?
Answer:
All things in satellite will be weightless.

Question 33.
Define the term displacement.
Answer:
The displacement of a moving particle in a given interval of time is the shortest distance between the two positions.

Question 34.
What do you mean by motion ?
Answer:
If a body changes its position with respect to time, the body is said to be in motion and that body is called kinetic body.

Question 35.
Define speed.
Answer:
Rate of change of position of a body with respect to time is known as its speed.

Question 36.
State SI unit of speed.
Answer:
SI Unit of speed is ms^-1.

Question 37.
Is velocity a scalar or a vector quantity ?
Answer:
Velocity is a vector quantity.

Question 38.
Define velocity.
Answer:
Rate of change of position of a body in particular direction with respect to time is called the velocity of the body.

Question 39.
Give one example of non-uniform velocity.
Answer:
When a train enters a station to stop, its velocity gradually decreases, while it leaves the station its velocity gradually increases.
In both the cases, velocity is unequal in equal time intervals i.e. the velocity of the train is non-uniform.

Question 40.
Define unbalanced forces.
Answer:
Unbalanced forces: When two forces of unequal magnitudes act in opposite directions on an object simultaneously, then the object moves inthe directions of the larger force. Such forces acting on the body are said to form a system of unbalanced forces.

Question 41.
State Newton’s first law of motion.
Answer:
Newton’s first law of motion : Every body continues in its state of rest or of uniform motion in a straight line unless it is acted on by some balanced force to change that state.

Question 42.
State Newton’s third law of motion.
Answer:
To every action there is an equal and opposite reaction.

Short answer type questions :

Question 1.
When a candle burns out, the molten wax weighs less than the candle. What happens to the ‘missing mass’?
Answer:
Explanation : The apparently missing mass of the candle converts to water vapour and carbon dioxide gas which disappears into air. The left out molten wax thus weighs less than the candle.

Question 2.
A thing is taken to Darjeeling from Kolkata. Is there be any change regarding its mass and weight?
Answer:
Explanation : Mass being intrinsic property of matter, it will remain same on both the places but weight being a force which is dependent on the value of ‘ g ‘ will be less at Darjeeling due to high altitude than that of Kolkata at sea-level.

Question 3.
Is there be any weight of a body falling freely on earth ? Give reasons.
Answer:
Force of attraction produces acceleration acting on a body falling freely towards the earth. In this condition acceleration due to gravity ‘ g ‘ will not act on the body. So, there will be no weight but the body will retain its mass because mass is the intrinsic property of matter.

Question 4.
Suppose the force of attraction of earth vanishes. What change would you see regarding mass and weight of a body?
Answer:
Explanation: The body will have its own mass but there will be no weight i.e. the body will be weightless.

Question 5.
Which is more fundamental, mass or weight ?
Answer:
Explanation : Mass is more fundamental than weight because mass remains unchanged at any place, whereas weight changes at different places on the Earth and on different planets.

Question 6.
What is the ultimate form of all energies ?
Answer:
Each form of energy ultimately transforms to heat energy directly or after some intermediate transformations.

Question 7.
Define matter.
Answer:
Matter : Matter is that which exists in nature occupying some space i.e. which have volume and mass and can be perceived by one or more of our senses. It exists in three states (a) solid (b) liquid (c) gas.

Question 8.
What do you mean by a body ?
Answer:
Body : Anything that is perceptible to our senses and has weight and free existence is called a body.
A body cannot change its state of motion of its own. A body is made up of matter.

Question 9.
What is energy ?
Answer:
Energy : Energy is that which exists in nature having no mass or does not occupy any space but can be perceived by our senses.

Question 10.
Define mass.
Answer: Mass : Mass is that intrinsic property of a body which determines the rate of change of state of motion in a straight line or of rest of the body when some external forces are applied on it.

Question 11.
What are the characteristics of mass ?
Answer:
Characteristics of mass :

1. It remains constant at any place of the universe, in any planet or any other place outside the universe.
2. It cannot be changed by the application of heat, by state of motion or rest, by electrification or magnetisation.
3. Mass of an object is its intrinsic property.

Question 12.
What is weight ?
Answer:
Weight : It is the force that a material body experiences towards the centre of the earth due to gravitational pull of the earth.

Question 13.
What is the relation between the mass and weight of a body ?
Answer:
Relation between the mass and weight of a body :
Weight of a body = mass of the body × acceleration due to gravity
If w be the weight of a body of mass ‘m’ and acceleration due to gravity be ‘g’ then, w = mg

Question 14.
What is acceleration due to gravity ?
Answer:
Acceleration due to gravity : The acceleration with which a freely falling body falls under the action of earth’s gravitational force is called acceleration due to gravity of the place and this is denoted by ‘g’.

Question 15.
What are the states of matter ?
Answer:
States of matter : There are three states of matter : solid, liquid and gas. Beside three states of matter there are two other states of matter, these are plasma state and super cooled liquid state.

Question 16.
Why can astronauts carry heavy loads on the moon but not on the earth ?
Answer:
The acceleration due to gravity on the moon is about onesixth than that on the earth. Astronauts can carry heavy loads easily on the surface of the moon, which is not possible on the earth.

Question 17.
State the law of conservation of mass.
Answer:
The law of conservation of mass (Lavoisier) : It states that the matter is neither created nor destroyed in a physical or chemical reaction i.e. the total mass of the components in a physical or chemical reaction remains unchanged after the reaction. The total mass of the universe is constant.

Question 18.
What do you mean by ‘energy’?
Answer:
Energy : Energy is defined as the capacity to perform work.
The amount of energy can be measured by the work done by the body. Its unit is same as the unit of work.

Question 19.
What is the law of conservation of energy ?
Answer:
Law of conservation of energy : The total amount of energy in this universe is constant. Energy cannot be created or destroyed. Energy can be transformed from one form to another.

Question 20.
What is solar pond technology ?
Answer:
Solar pond technology : In this technology, captured solar heat is kept at the bottom of a large expanse of saline water. Salty water layers are preventive to heat convection. Hot water from the bottom can be drawn whenever necessary and used for heating or forming electricity. In this way, solar ponds can form power regardless of whether the sun is out at the time.

Question 21.
What is Energy crisis ?
Answer:
Energy crisis : The limited stock of the common energy sources like coal, petroleum, natural gas cannot fulfill the demand of the huge requirements of energy for the large number of people and industry. But these sources are not infinitely large, they are going to be exhausted and cannot be renewed. These sources of non-renewable energy will be exhausted completely and the earth will face a great energy crisis.

Question 22.
What are non-conventional sources of energy ?
Answer:
Non-conventional sources of energy : To save the limited stock of coal, petroleum, scientists are in search of alternative sources of energy which are called non-conventional sources of energy. The main characteristic of these sources is that they are renewable. Some of these are (i) solar energy (ii) tidal energy.

Question 23.
State Einstein’s mass-energy equation.
Answer:
Einstein’s mass energy equation : The mass energy equivalence principle arises from Einstein’s famous theory of relativity.
Another form of energy is mass. Mass can be converted into energy and vice versa. If a mass ‘m’ can be converted completely into energy, then the amount of energy obtained from the equation.
E = mc²,(c = velocity of light in vacuum)

Question 24.
State the law of conservation of mass energy.
Answer:
Law of conservation of mass energy : In nature, the total amount of mass and energy is constant. Different types of transformation are possible between them. But mass and energy cannot be completely created or destroyed.

Question 25.
Discuss one simple example of conservation of mass in everyday life.
Answer:
Boiled rice has greater mass than that of the dry rice from which it is prepared. This happens because dry rice absorbs some water when boiled. So, total mass of dry rice and the absorbed water equals the mass of boiled rice.

Question 26.
Mention two differences between speed and velocity.
Answer:
Distinction between speed and velocity

Speed	Velocity
(i) Speed is the rate of change of position of a particle with respect to time.	(i) velocity is the rate of change of displacement of particle with respect to time.
(ii) Speed has only magnitude, so it is a scalar quantity.	(ii) Velocity has both magnitude and direction, so it is a vector quantity.

Question 27.
Define ‘newton’. Express it in CGS absolute unit.
Answer:
Newton : It is a force which when acting on a body of mass one kilogram produces in it an acceleration of one metre per second every second.
1 Newton = 1 kg × 1 ms²
= 1000 g × 100 cms²
= 10⁵ g.cms²
= 10⁵ dyne

Question 28.
What is frame of reference ?
Answer:
Frame of reference : It is any nearby or a distant fixed object from which the distance and position of a body is observed as time lapses.

Question 29.
What is meant by rest state of a body ?
Answer:
Rest state of body : A body is said to be at rest if it does not change its position with time from a fixed neighbouring object.

Question 30.
What is inertia of rest and what is inertia of motion ?
Answer:
Inertia of rest : The tendency of a body at rest to continue in that state is the inertia of rest.
Inertia of motion : The tendency of a body in uniform motion in a straight line to continue in that state is known as the inertia of motion.

Question 31.
State Newton’s second law of motion. What is dyne ?
Answer:
Newton’s second law of motion : When an unbalanced force acts on a body then the applied force is proportional to the acceleration produced in it.
Dyne : It is a force which when acting on an body of mass one gram produces in it an acceleration of one centimetre per second every second.

Broad answer-type questions :

Question 1.
Why does the value of ‘g’ vary from place to place?
Answer:
The value of ‘g’ varies from place to place :
(i) As we go up from earth’s surface or go down inside below the surface of the earth, the value of acceleration due to gravity decreases in both cases.
(ii) At the centre of the earth the value of acceleration due to gravity is found to be zero.
(iii) Moreover acceleration due to gravity changes due to earth’s spin about its axis also. Standard value of acceleration due to gravity is taken at 45° latitude at sea level.
(iv) Again on the surface of earth it is maximum at the pole. Because, due to orange shape of the earth, the distance of the pole is shorter than that of the equator from the centre of the earth.

Question 2.
Give an example of conservation of mass.
Answer:
Example : Burning of magnesium.
A small piece of magnesium ribbon is taken in the test tube and the stopper is tightly fitted. The test tube is filled with oxygen by replacing air in the test tube using the side tube and the delivery tube. The whole apparatus is weighed carefully. The test tube is now strongly heated on a bunsen burner. Magnesium ribbon burns brilliantly and after cooling a white residue remains in the test tube. The tube is again weighed. The weight of the test tube before and after heating is the same. The chemical reaction involves : 2 Mg + O₂ = 2 MgO. This proves the law of conservation of mass.

Question 3.
Write down the difference between mass and weight.
Answer:
Difference between mass and weight.

Mass	Weight
(i) The measure of inertia of a body in comparison to a standard body on the capacity of a body for gravitational attraction is the mass of the body.	(i) The force with which a body is attracted by the earth towards its centre is the weight of the body.
(ii) Mass of a body has only the magnitude, but no direction, so it is a scalar quantity.	(ii) Weight has both magnitude and direction and is therefore a vector quantity.
(iii) Mass of a body is its intrinsic property and it remains same everywhere.	(iii) Weight of a body is not its intrinsic property. The weight of a body depends upon the gravity of a place and it changes from place to place.
(iv) CGS and SI units of mass are gram (g) and kilogram(kg) respectively.	(iv) Absolute unit of weight in CGS system is Dyne and in SI system Newton. Gravitational units in CGS and SI are g-wt and kg-wt respectively.
(v) It is measured by an ordinary balance.	(v) It is measured by spring balance.
(vi) Mass of a body cannot be zero.	(vi) Weight of a body can be zero at the centre of the earth as ‘ g’ is zero there.

Question 4.
The sun is the most important source of energy on the earthExplain with Example.
Answer:
The sun is the most important source of energy on earth : After a few changes and transformations, almost all kinds of energy may be proved to originate from the sun.

Example : Let us Trace back the source of Hydel energy. The heat energy of solar radiation causes evaporation of water from different water bodies. This creates atmospheric water vapour. The water vapour forms cloud, rain, snow which are the sources of water for rivers. The river water is stored at an elevated position in dams. The water in dams possesses some kind of energy called potential energy. Falling water from the dams releases this energy forming another energy, known as kinetic energy. The kinetic energy of the falling water is used to rotate a turbine. The rotating turbine with the help of a generator produces hydel energy.

Question 5.
Discuss how wind energy and tidal energy may be utilised as sources of alternative energy.
Answer:
Wind energy : Wind mill or wind generator is used to produce electricity from air which has speed of at least 18 to 20 km / hr. The kinetic energy of wind is converted into the mechanical energy of the fans of the wind mill, which in turn runs the generator and produces electricity. Wind is the most pollution free energy for this reason. It is the world’s most rapidly developing new source of energy.

Tidal energy : In some coastal areas, the difference in water level between high tide and low tide is as high as 6 to 8 m. A portion of a river in such a region is blocked so that water in this part of river stores during high tide. This stored water gets potential energy. During low tide, the stored water is allowed to flow to lower level when the potential energy is transformed into kinetic energy which rotates a water turbine set on the path of water flow. The rotating turbine produces electric energy.

Question 6.
‘With the help of a common balance we measure the comparative mass of a body but not its weight’-Justify the statement.
Answer:
In a common balance, a body is counterpoised with standard units of mass, so mass of the body is comparatively measured. Acceleration due to gravity ‘ g ‘ acts equally on both the masses, so both the masses are equally pulled downwards by the earth. If the mass of the body is denoted as m and the standard mass be M, then we can write m g=M g that is m=M. Thus, in a common balance, mass of the body is determined in comparison with that of the standard weights. Weight of the body is not obtained in this process and that is why difference of weight of a body cannot be detected at different places with a common balance.

Question 7.
Give some examples of transformation of energy.
Answer:
Some examples of transformation of energy :

Question 8.
Deduce Newton’s first law of motion from the second law.
Answer:
From the relation, force = mass × acceleration (or retardation) if the applied force be zero i.e. in absence of any external force, acceleration or retardation is zero, since, mass cannot be zero. Now, acceleration or retardation is zero means, either the body is at rest or it is in uniform motion ; thus, in absence of an external force, a body is either at rest or in uniform motion, that is Newton’s first law of motion.

Question 9.
Why is it easier to accelerate a moving vehicle by push than one at rest ?
Answer:
Reason : When a car or a roller is at rest, to set it into motion, a large force is necessary to overcome the inertia of rest of its large mass and also to overcome its frictional force with ground. On the other hand, when it is already in motion, Since it itself tries to maintain its forward motion due to inertia of motion, a smaller effort can accelerate it.

Question 10.
How is the definition of force obtained from Newton’s first law of motion ?
Answer:
Newton’s first law of motion states that in absence of an external force the state of rest or of uniform motion of a body in a straight line does not change. Hence, force is an agent which acting on a body, either actually changes or tends to change the state of rest or uniform motion of the body in a straight line. This is the definition of force derived from Newton’s first law of motion.

Question 11.
If a ball is thrown straight upward by a passenger in a train running with uniform velocity it returns to his hand. Explain.
Answer:
Explanation : A ball thrown straight upward by a passenger in a train running with uniform velocity, returns to his hand although he has moved forward with the train. The ball which is also moving with the speed of the train, maintains its motion in the horizontal direction due to inertia of motion and returns to the hand.

Question 12.
What are the points in connection with action and reaction to be noted carefully ?
Answer:
The following points in connection with action and reaction are to be noted carefully.

1. Reaction exists as long as the action exists. In absence of action there will be no reaction.
2. Action and reaction between two bodies act along the straight line joining the bodies.
3. In nature, forces always exist in pairs. They never exist singly. A single isolated force is impossible.
4. Newton’s third law is applicable between two bodies irrespective of whether they are in motion or at rest, in contact or not.

Numerical Problems

Working formula:

(i) Weight of the body = mass of the body × acceleration due to gravity
= m × g
(ii) Value of ‘g’ on the surface of the moon
= \(\frac{1}{6}\) × value of ‘g’ on the earth
(iii) Average value of ‘ g ‘ on the earth’s surface in CGS system = 981 cm / sec² and in SI system = 9.81 m / sec²
(iv) Momentum of a moving body = mass of the body (m) × velocity of the body (v)
(v) (a) p = \(\frac{(m v-m u)}{t}\)
(b) p = m f.
[where p = force applied, m = mass of the body, u = initial velocity.
v = final velocity, t = time, f = acceleration]
(vi) Law of conservation of momentum :
m₁ u₁ + m₂ u₂ = m₁ v₁ + m₂ v₂

Example 1 : The reading in a spring balance of a body of mass 20 kg is found to be 196 newton. What is the value of acceleration due to gravity of the place?
Answer:
We know, w = m × g
or, g = \(\frac{w}{m}\)
or, g = \(\frac{196}{20}\) = 9.8 m / s²
w = weight of the body
= 196 N
m = mass of the body
= 20 kg
g = acceleration due to
gravity = ?
So, the acceleration due to gravity = 9.8 m / s²

Example 2 : What will be the weight of a body of mass 200 g at a place where g = 980 cm / sec 2.
Answer:
We know,
w = m × g
∴ w = 200 × 980 g . cm / sec²
= 196000 dyne

So, the weight of the body = 196000 dyne

w = weight of the
body = ?
m = mass of the body
= 200 g
g = acceleration due
to gravity
= 980 cm / sec²

Example 3: What will be the weight of a body on the surface of the moon which weighs 240 kg on the earth?
Answer:
We know,
Value of ‘ g ‘ on the surface of the moon = \(\frac{1}{6}\) × value of ‘ g ‘ on the earth
So, the weight of the body on moon = \(\frac{1}{6}\) × 240 kg = 40 kg

Example 4 : A body has mass 20 kg. What will be the weight of the body ? (g = 9.81 m / sec 2)
Answer:
We know, w = m × g
or, w = 20 × 9.81 kg-m / sec²
∴ w = 196.2 Newton
So, the weight of the body

w = weight of the
body = ?
m = mass of the body = 20 kg
g = 9.81 m / sec²
= 196 . 2 newton.

Example 5 : A body has mass 30 kg on the earth. What will be the mass and weight of the body in artificial satellite of the earth ?
Answer:
In artificial satellite of the earth the mass of the body will be same i.e. the mass of the body will be 30 kg.
The weight of the body will be zero in artificial satellite of the earth.

Example 6 : What will be the magnitude of the force acting on a mass of 10 kg to produce an acceleration of 4 m / s 2 ?
Answer:
We know,
p = m × f
∴ p = 10 × 4 = 40 Newton
m = 10 kg
f = 4 m / s²
p = ?
∴ The force required is 40 Newton

Example 7 : Calculate the acceleration of a body of 250 g when acted upon by a force of Q 1 Newton,
Answer:
We know, p = m × f
Or, f = \(\frac{p}{m}\) = \(\frac{1}{0.25}\) = 4 m / s²
p = 1 N
m = 250 g
= 0.25 kg
f = ?

Example 8: A force is acting on a mass of 20 g. The initial velocity of the particle is 10 cm / s. After 5 s, the velocity is increased to 40 cm / s. Find the magnitude of the force.
Answer:
We know,
v = u + f t
∴ f t = v – u
or, f = \(\frac{40-10}{5}\) = 6 cm / s²
We also know,
p = m × f
= 20 × 6 = 120 dyne.
u = 10 cm / s
m = 20 g
v = 40 cm / s
t = 5 s
f = ?
m = 20 g
f = 6 cm / s²
p = ?

Example 9 : A force of a 4 kg-wt acts on a body of mass 9.8 kg.
Calculate the acceleration.
(Take g = 9.8 m / s² )
Answer:
We know,
4 kg-wt = 4 kg × 9.8 m / s² = 39.2 N
Now, force = mass × acceleration
∴ acceleration = \(\frac{\text { force }}{\text { mass }}=\frac{39.2 \mathrm{~N}}{9.8 \mathrm{~kg}}\)
= 4m / s²

Example 10 : What will be the acceleration of a body of mass 15 kg when a force of 45 newton is applied on it ?
Calculate the acceleration.
Answer:
We know,
p = m / f
m = 15 kg
p = 45 N
f = ?
or,
f = \(\frac{p}{m}\)
= \(\frac{45}{15}\) = 3m / s²

Example 11 : A car is initially moving with an acceleration of 1.8 m / s². After some time the driver accelerates the car and it moves with an acceleration of 2.7 m / s². What is the ratio of the force exerted by the engine in the two cases?
Answer:
In the first case,
the force,
p₁ = mass × acceleration
= m × 1.8 N(m = mass of the car )
In the second case, the force
p₂ = mass × acceleration
= m × 2.7 N
∴ \(\frac{p_1}{p_2}=\frac{m \times 1.8}{m \times 2.7}=\frac{2}{3}\)

Example 12 : Equal forces act on two masses m and 2 m. If the acceleration acquired by m be f, what is the acceleration acquired by 2 m ?
Answer:
From the relation, force = mass × acceleration, the force acting on the mass m is m f.
Now the same force m f acts on the mass 2 m, and since acceleration = \(\frac{\text { force }}{\text { mass }}\) , the acceleration of the second body = \(\frac{m f}{2 m}=\frac{f}{2}\)

Detailed explanations in West Bengal Board Class 9 Physical Science Book Solutions Chapter 6 Heat offer valuable context and analysis.

WBBSE Class 9 Physical Science Chapter 6 Question Answer – Heat

Very short answer type questions

Question 1.
What is the unit of heat in CGS system ?
Answer:
Calorie is the unit of heat in CGS system.

Question 2.
What is the unit of heat in SI system ?
Answer:
In SI system, the unit of heat is Joule.

Question 3.
What is steam point?
Answer:
Steam point is the boiling point of water under normal pressure.

Question 4.
What is 1 calorie?
Answer:
1 calorie is defined as the heat required to raise the temperature of lg of water through one degree Celsius.

Question 5.
What is the unit of specific heat in CGS system ?
Answer:
The unit of specific heat in CGS system is cal/g/°C

Question 6.
What is the unit of specific heat in SI system ?
Answer:
The unit of specific heat in SI system is J/kg/K.

Question 7.
What is fundamental interval ?
Answer:
It is the range of temperature between the upper and lower fixed points in the scale of temperature.

Question 8.
What are the scales of temperature ?
Answer:
There are three scales of temperature —

• Celsius scale
• Fahrenheit scale &
• Kelvin scale.

Question 9.
What is the value of 100°C in Fahrenheit scale ?
Answer:
In Fahrenheit scale the temperature is 212°F.

Question 10.
What are the factors for determining the quantities of heat in a body ?
Answer:
The quantity of heat depends upon the following factors :

• temperature
• mass and
• material of the body.

Question 11.
Is heat a vector quantity ?
Answer:
No, heat is a scalar quantity.

Question 12.
What is the relation between calorie and joule ?
Answer:
1 calorie = 4.18 joule

Question 13.
What is the principle of calorimetry ?
Answer:
The principle of calorimetry is :
Heat absorbed by the cold body
= Heat given out by the hot body.

Question 14.
Is there any change of temperature during the change of state ?
Answer:
There is no change of temperature during the change of state.

Question 15.
Which temperature is lower — 0°C or 0°F ?
Answer:
0°F is lower than 0°C.

Question 16.
What are the lower fixed point and upper fixed point of thermometer in Celsius scale ?
Answer:
Lower fixed point is 0°C and upper fixed point is 100°C.

Question 17.
What are the lower fixed point and upper fixed point of thermometer in Fahrenheit scale ?
Answer:
Lower fixed point is 32°F and upper fixed point is 212°F.

Question 18.
What is the fundamental interval of Celsius scale ?
Answer:
The fundamental interval is divided in 100 equal parts in Celsius scale.

Question 19.
What is the fundamental interval of Fahrenheit scale ?
Answer:
The fundamental interval is divided into 180 equal parts in Fahrenheit scale

Question 20.
What is the melting point of ice in Kelvin scale ?
Answer:
Melting point of ice in Kelvin scale is 273K.

Question 21.
What type of scale is used in clinical thermometer ?
Answer:
Generally Fahrenheit scale is used in clinical thermometer.

Question 22.
Which temperature is same in both Celsius scale and Fahrenheit scale ?
Answer:
– 40° temperature will read same both in Celsius scale and Fahrenheit scale.

Question 23.
Which substance has the highest specific heat ?
Answer:
Water has the highest specific heat.

Question 24.
What is specific heat capacity ?
Answer:
The specific heat in SI system is called specific heat capacity.

Question 25.
What is the value of specific heat capacity of pure water ?
Answer:
The specific heat capacity of pure water is 4200 J/kg/K.

Question 26.
Is specific heat of solid greater than that of liquid ?
Answer:
Generally specific heat of solid has lower value than that of liquid.

Question 27.
What is the normal temperature of human body ?
Answer:
The normal temperature of human body is 98-4°F or 36-9°C.

Question 28.
If a substance has thermal capacity 100 calorie, what will be its water equivalent ?
Answer:
If the substance has thermal capacity 100 calorie, then water equivalent of the substance will be 100 g.

Question 29.
What is the relation between Celsius scale and Kelvin scale ?
Answer:
If a temperature in Kelvin scale is T K and the temperature in Celsius scale is t°C, the relation is :
TK = 273 + t°C

Question 30.
Give an advantage of use of mercury in thermometer.
Answer:
Equal volume of mercury increases or decreases for each degree increase or decrease of temperature in a regular manner.

Question 31.
The specific heat of copper is 0.09. What does the statement mean ?
Answer:
‘Specific heat of copper is 0-09’ means that 0 09 calorie of heat is required to raise the temperature of lg of copper through 1°C.

Question 32.
What is the value of 30°C in Kelvin scale ?
Answer:
The given temperature of is 303 K in Kelvin scale.

Question 33.
What is the boiling point of water in Kelvin scale ?
Answer:
The boiling point of water in Kelvin scale is 373 K.

Question 34.
By which process, heat reaches the earth from the sun ?
Answer:
Radiation.

Question 35.
What is heat ?
Answer:
It is an external agency whose absorption turns a body hot and extraction turns a body cold.

Question 36.
What is temperature ?
Answer:
The thermal condition of a body which determines whether heat will flow from the body to another body in contact or not is called the temperature of the body.

Question 37.
Define thermal capacity.
Answer:
Thermal capacity of a body is the quantity of heat required to raise the temperature of the body through one degree.

Question 38.
What is the unit of thermal capacity ?
Answer:
In CGS system the unit of thermal capacity is calorie per degree Celsius and in SI system it is joule per degree kelvin.

Question 39.
What are the value of latent heat of fusion of ice in SI and CGS system ?
Answer:
The values of latent heat of fusion of ice in SI system and CGS systems are 3.36 × 10⁵ Jkg^-1 and 80 cal g^-1 respectively.

Question 40.
Does saturated vapour obey Boyle’s law ?
Answer:
Saturated vapour does not obey Boyle’s law.

Question 41.
Does unsaturated vapour obey pressure law ?
Answer:
Unsaturated vapour obeys pressure law.

Question 42.
At what temperature is the density of pure water become maximum ?
Answer:
4°C

Question 43.
Can a certain quantity of unsaturated vapour be made saturated ?
Answer:
A certain quantity of unsaturated vapour can become saturated if the pressure be increased or the temperature be decreased at constant volume.

Question 44.
State two favourable conditions for formation of dew.
Answer:
The favourable conditions for the formation of dew are –

• Clear sky and
• still air

Short answer type questions

Question 1.
What is heat ?
Answer:
Heat : It is an external agency whose absorption turns a body hot and extraction turns a body cold.

Question 2.
What are the types of heat ?
Answer:
Types of heat : There are three types of heat. These are :

• sensible heat
• latent heat
• radiant heat

Question 3.
What is sensible heat ?
Answer:
Sensible heat: It is the type of heat that is perceptible by senses. This causes rise of temperature of a body that can be measured with a thermometer.

Question 4.
What is latent heat ?
Answer:
Latent heat: It is the quantity of heat absorbed or released when a substance of unit mass undergoes a physical change of state at a constant temperature and pressure. This heat is not detectable with a thermometer.

Question 5.
What is radiant heat ?
Answer:
Radiant heat : It transmits from a source of heat in all directions with the speed of light and in the form of waves.

Question 6.
What is temperature ?
Answer:
Temperature : The temperature of a body is that thermal condition of the body which determines whether it will absorb heat from other body or release heat to that body when they are kept in close contact.

Question 7.
What is lower fixed point of a thermometer ?
Answer:
Lower fixed point of a thermometer : At normal atmospheric pressure, the temperature at which pure ice melts into water or pure water freezes into ice is called the lower fixed point of a thermometer.

Question 8.
What is upper fixed point of a thermometer ?
Answer:
Upper fixed point of a thermometer : It is the temperature at which pure water boils and transforms into steam under normal atmospheric pressure.

Question 9.
What do you mean by fundamental interval ?
Answer:
Fundamental interval : The range of temperature between the upper and the lower fixed points is scalled Fundamental interval.

Question 10.
What do you mean by Celsius scale of temperature ?
Answer:
Celsius scale of temperature : In this scale the lower fixed point is 0°C and the upper fixed point is 100°C. The fundamental difference is divided into hundred equal parts and each parts represents 1° Celsius.

Question 11.
What do you mean by Fahrenheit scale of temperature ?
Answer:
Fahrenheit scale of temperature : In this scale the lower fixed point is 32°F and the upper fixed point is 212°F. The fundamental difference is divided into 180 equal parts and each part represents 1°F.

Question 12.
What is absolute scale or Kelvin scale of temperature ?
Answer:
Absolute or Kelvin scale of temperature : In this scale the lower fixed point is 273K and the upper fixed point is 373K. The fundamental interval is divided into 100 equal divisions like that in the Celsius scale. Each division represents 1K.

Question 13.
What are the units of heat in CGS and SI system ?
Answer:

• Unit of heat in CGs system is calorie : It is the amount of heat required to raise the temperature of one gram of pure water through 1°C.
• Unit of heat in SI system is joule : As heat is a form of energy so nowadays heat is measured in the unit of energy. That is heat is expressed in joule. It is the SI unit of heat.
  1 calorie = 4.18 joule.

Question 14.
What do you mean by specific heat of a substance ?
Answer:
Specific heat of a substance : It is defined as the quantity of heat required to raise the temperature of unit mass of it by 1 degree.

Question 15.
What is specific heat capacity of a substance ?
Answer:
Specific heat capacity of a subsance : The specific heat in SI system is known as specific heat capacity.
Definition : Specific heat capacity of a substance is the quantity of heat required to raise the temperature of 1 kilogram of the substance through 1K.

Question 16.
What are the units of specific heat in CGS and SI system ?
Answer:
Unit of specific heat in CGS system is : cal/g/°C
Unit of specific heat in SI system is : J/kg/K

Question 17.
‘The specific heat of copper is 0.09’ – What does the statement mean ?
Answer:
The statement that ‘the specific heat of copper is 0-09’ means that 0.09 units of heat (calorie) is required to raise the temperautre of unit mass (1g) of copper through one degree (1°C)

Question 18.
What is thermal capacity or heat capacity of a body ?
Answer:
Thermal capacity or heat capacity of a body : It is defined as the quantity of heat needed to raise the temperature of the body for unit degree rise of temperature.

Question 19.
What are the units of heat capacity in CGS system and SI system ?
Answer:
Unit of heat capacity in CGS system is : Calorie/°C.
Unit of heat capacity in SI system is : Joule/kelvin

Question 20.
Deduce the relation between thermal capacity and specific heat of a body
Answer:
Relation between thermal capacity and specific heat of a body :
Quantity of heat required to raise the temperature of a body of mass
‘m’ and specific heat s by 1° = m.s.1 = m.s
i.e. Thermal capacity = ms
or, Thermal capacity = mass x specific heat

Question 21.
Show that specific heat is the heat capacity of unit mass.
Answer:
Thermal capacity of a body
= mass x specific heat of material of the body
Hence, thermal capacity = ms
Putting, m = 1, in the above relation,
Thermal capacity Specific heat
So, it can be concluded, specific heat is the thermal capacity per unit mass.

Question 22.
What is water equivalent ?
Answer:
Water equivalent: The water equivalent of a body is the mass of water which will be heated through one degree by the amount of heat required to raise the temperature of the body through one degree.

Question 23.
What are the units of water equivalent in CGS and SI system ?
Answer:
Unit of water equivalent in CGS system is : gram (g).
Unit of water equivalent in SI system is : Kilogram (kg)

Question 24.
What are the differences of thermal capacity and water equivalent ?
Answer:
Differences of thermal capacity and water equivalent

Thermal capacity	Water equivalent
(i) Thermal capacity represents some quantity of heat. (ii) Units of thermal capacity in CGS and SI system are calorie/°C and J/K respectively.	(i) Water equivalent repre­sents some quantity of water. (ii) Units of water equivalent in CGS and SI system are gram and kg respectively.

Question 25.
What is the fundamental principle of calorimetry ?
Answer:
Fundamental principle of calorimetry :
If no heat flows to outside from the system of bodies and if no chemical reaction takes place between them, then from the principle of conservation of energy, it can be said,
heat lost by the hotter body = heat gained by the colder body.
This is the principle of calorimetry.

Question 26.
What is the relation between heat and molecular velocity ?
Answer:
Relation between heat and molecular velocity : The molecules in a hotter body have more rapid motion and those of a less hot body have slower motions. Also, if heat is supplied to a body, its molecules move more rapidly. If heat is withdrawn from a body the motion of its molecules becomes slower. Thus, increase or decrease of melecular velocity corresponds to higher or lower quantity of heat.

Question 27.
Why should the bore of a thermometer be uniform ?
Answer:
Reason: The bore should be uniform, otherwise, unequal expansion of mercury thread will take place at different parts of the bore for equal change of temperature.

Question 28.
What is meant by sensitivity of a thermometer ?
Answer:
Sensitivity of a thermometer : A thermometer is considered to be sensitive if it :

• quickly picks up the temperature of the body with which it is kept in contact
• can detect small changes of temperature.

Question 29.
Why should the bore of a thermometer be narrow ?
Answer:
Reason : The bore of thermometer tube should be narrow so that expansion of mercury thread is long enough for a small change of temperature.

Question 30.
Why is water preferred than other liquids in a hot water bag ?
Answer:
Reason: Since water has the highest specific heat, a certain mass of water heated to a certain temperature contains more heat than the same mass of any other liquid heated to the same temperature. So, hot water will take longer time to cool than any other liquid heated to the same temperature. So, for hot compression it can be used for sufficiently long time.

Question 31.
What does the first law of thermodynamics state ?
Answer:
First law of thermodynamics :
When work is completely converted into heat or heat is completely converted into work, one is equivalent to the other.
Mathematical expression of first law of thermodynamics :
If by converting work W completely heat H is obtained then W α H
or W = JH (J = mechanical equivalent of heat)

Question 32.
What is mechanical equivalent of heat ? What are the units of mechanical equivalent of heat in CGS and Si system ?
Answer:
Mechanical equivalent of heat : Work done to produce unit amount of heat is called mechanical equivalent of heat.
Unit of mechanical equivalent of heat :
CGS system: 4 18 x 10⁷ erg/cal
SI system : 4 18 J/Cal

Broad answer type questions

Question 1.
What are the differences between heat and temperature ?
Answer:
Difference between Heat and Temperature :

Heat	Temperature
(i) Heat is a form of energy.	(i) Temperature indicates the thermal condition or degree of hotness or coldness of a body.
(ii) When a body absorbs heat, its temperature, in general, rises i.e. heat is the cause of temperature.	(ii) Temperature is the effect of heat.
(iii) Equal quantities of heat in two bodies do not signify equal temperature.	(iii) Equal temperature of two bodies does not signify equal heat in them.
(iv) During change of state of matter, total amount of heat alters.	(iv) During change of state, temperature remains unaltered.

Question 2.
What are the advantages of mercury as a thermometric substance?
Answer:
Advantages of mercury as a thermometric substance :

• Mercury being a metal, it absorbs very little heat from the source and thus there is almost no change in temperature of the source.
• Mercury is a shinning liquid, so can be easily seen through glass.
• Mercury remains in liquid state for long range of temperature (-39°C to 357°C). So temperature can be measured to a long range.
• Mercury does not wet the glass wall of tube, so it can move up and down easily through the glass tube.

Question 3.
What steps should be taken to make a thermometer sensitive ?
Answer:
Requisites of a sensitive thermometer :

• The thermometer bulb should have thin walls, so that heat from
  a body in its contact may easily reach the mercury inside it.
• The bore of thermometer-tube should be narrow so that expansion of mercury thread is long enough for a small change of temperature.
• The bore should be uniform, otherwise, unequal expansion of mercury thread will take place at different parts of the bore for equal change of temperature.
• The thermometric liquid should be good conducting so that it quickly assumes the temperature of the body in contact of the thermometer.

Question 4.
Obtain an expression for the heat absorbed or given out by a body.
Answer:
Calculation of amount of heat absorbed or given out by a body :
If S be the specific heat of substance, then we can write from the definition of specific heat that,
1 unit mass of a substance for 1° rise or fall of temperature will absorb or give out ‘s’ units of heat.
∴ m unit mass of a substance for t° rise or fall of temperature will absorb or give out ‘mst’ units of heat. That is,
Quantity of heat (absorbed or given out)
= mass of the body x specific heat × rise or fall of temperature.

Question 5.
What is the relation between Celsius, Fahrenheit and Kelvin scales ?
Answer:
Relation between Celsius, Fahrenheit and Kelvin scales:
Since the range of temperature from lower fixed point to upper fixed point is equal in all three scales, 100 centigrade degrees = (212 – 32) or 180 Fahrenheit degree = (373 – 273) or 100 absolute degrees.
We consider three thermometers in the above three scales are dipped simultaneously in a liquid of certain temperature. Let the temperatures recorded in the Celsius, Fahrenheit and Kelvin thermomters respectively be C, F, and K. Now it can be proved that

Question 6.
Equal masses of milk and water are separately taken in two identical vessels. The vessels are heated simultaneously on the same oven. Which one will have quicker rise of temperature — milk or water and why ?
Answer:
Explanation: Specific heat of milk is less than that of water, so milk will require a smaller quantity of heat for each degree rise of temperature that needed for the same mass of water. So, supply of heat being same to the equal masses of milk and water, rise of temperature of milk will be quicker than that of water.

Numerical problems

Working formula :

\(\frac{C}{5}=\frac{F-32}{9}=\frac{K-273}{5}\)
(Let the temperatures recorded in the Celsius, Fahrenheit and Kelvin thermometers respectively be C, F and K)

(ii) \(1^{\circ} \mathrm{C}=\frac{9^{\circ}}{5} \mathrm{~F} ; 1^{\circ} \mathrm{F}=\frac{5^{\circ}}{9} \mathrm{C}\)

(iii) Relation between temperatures of any two scales, X and Y :
\(\frac{\text { Reading in } X-\text { Lower fixed point of } X}{\text { Fundamental interval of } X}\)
\(=\frac{\text { Reading in } Y-\text { Lower fixed point of } Y}{\text { Fundamental interval of } Y}\)

(iv) Thermal capacity = ms (m = mass of the body ; s = specific heat)

(v) Water equivalent = ms

(vi) Quantity of heat (absorbed or given out) = ms (t₂ – t₁)
(m – mass ; s = specific heat ;
t₁ and t₂ are two different temperature)

(vii) Principle of calorimetry :
Heat lost by the hotter body = Heat gained by the colder body

(viii) W = JH (W = work done, H = heat produced, J = mechanical equivalent of heat)

Problem 1.
The temperature on a day was 94°F. What is it in celsius scale?
Answer:
We Know that

Problem 2.
The lowest attainable temperature so far is – 270° celsius. What is it in Fahrenheit scale?
Answer:
C = -270°
F = ?
We know,

or, F – 32 = – 54 x 9 = – 486
or, F= – 486 + 32 – 454
∴ F= – 454°

Problem 3.
Convert 50°C in Fahrenheit scale.
Answer:
C= 50°
We know,

or, F – 32 = 10
or, 90F – 32 × 9
or, F= 90 + 32 = 122
Hence, 50°C = 122°F.

Problem 4.
The rise in temperature of a body is 600 in celsius scale. What is the corresponding rise in temperature in Fahrenheit scale?
Answer:
We know, 1°C = \(\frac{9}{5}\)°F
∴ 60°C = (\(\frac{9}{5}\) x 60)°F = 108°F

Problem 5.
The difference in the readings of a Fahrenheit and a Celsius thermometer is 480. What are the actual readings shown in the thermometers ?
Answer:
Let the actual readings in the Fahrenheit and the Celsius thermometers correspond to F and C.
∴ F – C= 48° or, F = C+ 48°
Again, from the relation,

or, 9C = 5C + 80 or, 4C 80 or, C = 20
Now, F = C + 48° = 20° + 48° = 68°

Problem 6.
A certain temperature is 104°F, what is its value in Kelvin scale ?
Answer:
We know the relation between Fahrenheit and Kelvin scale is

Problem 7.
A thermometer having the corresponding upper and lower fixed points 95° and 15°, reads a temperature 65°. What will this temperature be in Celsius scale ?
Answer:
The relation between temperature of celsius and the given scale can be written from the general relation between any two scales as,

∴ The required temperature is 625°C.

Problem 8.
The normal temperature of human body is 98 4°F. What is the value of this temperature in centigrade scale ?
Answer:
We know,

So the required temperature = 3689°C.

Problem 9.
How much calorie of heat would be produced by converting 42 Joule of work completely into heat?
Answer:
We know, W = JH
or, \(\mathrm{H}=\frac{W}{J}=\frac{42 \mathrm{Joule}}{4 \cdot 2 \mathrm{Joule} / \mathrm{cal}}=10 \mathrm{cal}\)

Problem 10.
Which temperature is same in both Centigrade scale and Fahrenheit scale ?
Answer:
Let the temperature be x°
According to the question, C = F = x
We know,

or, x = \(\frac{-160}{4}\) = – 40
So, – 40° temperature will read same both in Fahrenheit and Centigrade scale.

Problem 11.
Mass and specific heat of a substance is 100g and 0.09 respectively. Find the thermal capacity and water equivalent of
the body.
Answer:
We know,
m = 100g; s = 0.09
Thermal capacity = ms
= 100 × 0.09 cal/°C
Water equivalent = ms
= 100 × 0.09 = 9g

Problem 12.
Calculate the amount of heat required to raise the temperature of 60g of water from 20°C to the boiling point.
Answer:
m = 50g
t₁ = 20°C
t₂ = 100°C
s = 1
We know,
Absorbed heat = ms (t₂ – t₁)
50 × 1 × (100 – 20)
= 50 × 80
= 4000 cal

Problem 13.
A body of iron having mass 60 g is cooled from 200°C to 100°C. Calculate the amount of heat given out. Specific heat of iron = 0.12.
Answer:
m = 60g
t₁ = 100°C
t₂ = 200°C
S = 0.12
We know,
the amount of heat given out by iron =
= ms (t₂ – t₁)
= 60 × 0.12 (200 –  100)
= 60 × 0.12 × 100 = 720 cal

Problem 14.
300 g lead at 99°C is dropped in 100 g water at 18°C. The final temperature of the mixture is 27°C. Find the specific heat capacity of lead if specific heat capacity of water is 4200 J kg-1 K-1.
Answer:
Let the specific heat capacity of lead be ‘s’ J/kg/K.
Heat lost by 300 g lead to reach the temperature to 27°C
= \(\frac{300}{1000}\) = × s × (99 – 27) J
= 0.3 × s × 72 Joules = 21.6s J
Heat gained by 100 g water when the temperature rises from 18°C to 27°C
= 100 × 42000 × (27 – 18) J = 3780 J.
So, from the principle of calorinetry, heat lost heat gained
∴  21.6s = 3780
or, s = \(\frac{3780}{21 \cdot 6}\) 175 JKg-1 K-1

Problem 15.
A piece of copper heated to 35°C is dropped into 140 g of water at 15°C. The mass of copper is 150 g and the specific heat of copper is 400 J/kg/K. Find the final temperature. (Specific heat of water = 4200 J/kg/K)
Answer:
Let the final temperature be t°C.
Now, the heat lost by copper.
= 0.15× 400 × (35 – t) = 60 (35 – t)J
Heat gained by water
= 0.14 × 4200 × (t – 15) = 588 (t – 15) J
So, from the principle of calorimetry,
heat lost = heat gained
∴ 60 (35 – t) = 588 (t -15)
or, 60 × 35 – 60t = 588 t – 588 × 15
or, 60 × 35 + 588 × 15 = 588t + 60t
∴ 648t = 60 x 35 + 588 x 15
or, t =\(\frac{60 \times 35+588 \times 15}{648}\) = 16.85°C

Detailed explanations in West Bengal Board Class 9 Physical Science Book Solutions Chapter 7 Sound offer valuable context and analysis.

WBBSE Class 9 Physical Science Chapter 7 Question Answer – Sound

Very short answer type questions

Question 1.
How is the sound produced when we speak ?
Answer:
Sound is produced due to vibration of our vocal chord.

Question 2.
How does the velocity of sound depend on pressure ?
Answer:
Velocity of sound is independent of change of pressure.

Question 3.
What is musical sound ?
Answer:
It is a pleasing sound produced by a periodically vibrating body.

Question 4.
How does intensity of sound depend on density of medium ?
Answer:
Intensity of sound increases in a denser medium than in a rarer medium.

Question 5.
What is note of sound ?
Answer:
It is a sound of mixed frequencies.

Question 6.
What are the characteristics of a musical sound ?
Answer:
Characteristics of a musical sound are, it has

• Intensity
• Pitch
• Quality or Timbre

Question 7.
Which characteristic of musical sound depends on frequency ?
Answer:
Pitch depends on frequency.

Question 8.
Find the optical analogous of note and tone,
Answer:
Note is analogous to white or polychromatic light and tone is analogous to light of a single colour.

Question 9.
What is fundamental tone ?
Answer:
In a note, the sound of least frequency is known the fundamental tone.

Question 10.
What should be the frequency of audible sound ?
Answer:
We can hear sound only if the number of vibrations per second, called, frequency of a vibrating body lies within the limit 20 to 20,000.

Question 11.
Between a plane mirror and a wail of house, which one will reflect sound?
Answer:
A wall of house will reflect sound.

Question 12.
What is the minimum distance of the reflector to produce an echo ?
Answer:
The minimum distance of the reflector is 16.6 m to produce an echo.

Question 13.
What is Hertz ?
Answer:
The unit, used at present to express frequency is Hertz (Hz) named after the celebrated German physicist Heinrich Hertz.

Question 14.
What is decibel ?
Answer:
Decibel (dB) is the unit of expressing intensity of sound.

Question 15.
The oscillation of a pendulum cannot be heard. Why ?
Answer:
The oscillation of a pendulum has a frequency less than 20 Hz. So, we cannot hear the sound of Oscillation.

Question 16.
State the relation among velocity, wavelength and frequency of a wave.
Answer:
Wave velocity = Frequency x Wavelength

Question 17.
What is the unit of frequency ?
Answer:
Unit of frequency is cycles/second or CPS or Hz.

Question 18.
What is the unit of wavelength in SI system ?
Answer:
The unit of wavelength in SI system is metre.

Question 19.
What is the velocity of sound at 0°C ?
Answer:
332 m/sec.

Question 20.
Is medium required for the propagation of sound ?
Answer:
Medium is required for the propagation of sound.

Question 21.
Which is responsible for the generation of sound ?
Answer:
Vibration is responsible for the generation of sound.

Question 22.
How does pitch depend on frequency ?
Answer:
Greater the frequency, higher will be the pitch.

Question 23.
Can sound travel through vacuum ?
Answer:
Sound cannot travel through vacuum.

Question 24.
How many frequencies are there in a tone ?
Answer:
A tone is a sound of single frequency.

Question 25.
What is called fundamental tone ?
Answer:
In a note the tone of lowest frequency is called the fundamental tone.

Short Answers type Questions Marks for each 2

Question 1.
What is the definition of sound ?
Answer:
Sound: Sound is a type of energy, which is generated from a vibrating body, and which travels through an elastic medium and finally reaches our ear to create a special sensation in the brain.

Question 2.
How is the sound produced ?
Answer:
The material bodies capable of producing sound are called the sources of sound or sounding bodies. Sound is produced due to vibrations of the sounding bodies.

Question 3.
What is ultrasonic sound ?
Answer:
Ultrasonic sound : We cannot hear sound generated from the sources having frequency 20,000/sec or more. These sounds are known as ultrasonic sound.

Question 4.
What is subsonic sound ?
Answer:
Subsonic sound : We cannot hear the sound generated from the sources having frequency 20/sec or less. These sounds are known as subsonic sound.

Question 5.
What is audible sound ?
Answer:
Audible sound : We can hear only the sounds of the sources producing about 20 to 20,000 vibrations per second. These sounds are called audible sound.

Question 6.
Can sound travel through vacuum ?
Answer:
Explanation : For propagation of sound, a material medium (solid, liquid or gas) is necessary. Sound cannot travel through vacuum.

Question 7.
If a person talks or even screams on the surface of the moon, the sound will not be audible. Explain why.
Answer:
Explanation : The moon has no atmosphere or gas surrounding the moon. It is absolutely vacuum all around the moon. That is why if a person talks or even screams on the surface of the moon, the sound will not be audible.

Question 8.
Define wave.
Answer:
Definition of wave : It is defined as a disturbance that moves through a medium transferring energy from a point to another point without any physical transportation of the material between the points.

Question 9.
What is transverse wave ?
Answer:
Transverse wave: Transverse wave motion is that wave motion in which the individual particles of the medium execute vibrations about their mean positions in a direction perpendicular to the direction of motion of the wave.

Question 10.
What is longitudinal wave ?
Answer:
Longitudinal wave : Longitudinal wave motion is that wave motion in which the individual particles of the medium execute vibrations about their mean positions along the direction of motion of wave.

Question 11.
What do you mean by oscillation ?
Answer:
Oscillation: An oscillation of a particle is its trajectory in which the particle starting from a certain position moves through some distance and retracing the path it returns to its starting point with the same direction of motion with which it started initially.

Question 12.
What do you mean by amplitude ?
Answer:
Amplitude: The maximum displacement of a particle in a medium on either side of its mean position is called amplitude.

Question 13.
What is time period ?
Answer:
Time period : The time required by a particle to make one complete oscillation is known as time period. It is denoted by T.

Question 14.
What is frequency ?
Answer:
Frequency : The number of complete oscillations of a source of sound per second is known as its frequency.
Unit of frequency is Hertz, its symbol is Hz.

Question 15.
What do you mean by wavelength ?
Answer:
Wave length :

• It is the distance a wave or an energy travels through during one complete oscillation of its source.
• It is the distance between the two consecutive crests or troughs in a wave.
  It is normally represented by A. Its SI unit is metre (m).

Question 16.
What is wave velocity ?
Answer:
Wave velocity : In a medium, the distance travelled by the wave in one second is defined as the velocity of propagation of the wave or wave velocity. It is normally represented by c.

Question 17.
Establish a relation connecting wave velocity, wavelength and frequecy.
Answer:
Relation among wave velocity, wavelength and frequency :
Let the frequency and wavelength of a wave be v and λ respectively.
According to the definition :
‘v’ numbers of complete waves are generated in 1 sec. Since wavelength is λ, so in 1 sec, wave advances by v x λ = vλ distance.
Now, the distance traversed by wave in 1 sec is its velocity (v).
So,v = vλ
∴ Wave velocity = Frequency x Wavelength
This equation is applicable for all types of waves.

Question 18.
What do you mean by free or natural vibration ?
Answer:
Free or Natural vibration : When a body vibrates with its own natural frequency, it is said to execute natural or free vibrations. The frequency of free vibration depends on the density, shape and elasticity of the body.
Example : The frequency of a tuning fork depends on the length and cross-section of its arms as well as density and elasticity of the material of tuning fork.

Question 19.
What is called forced vibration ?
Answer:
Forced vibration: When a body is maintained in a state of vibration by a strong periodic force, the vibration is called forced vibration.

Example : Intensity of sound generated from a tuning fork is not very high and hence cannot be heard from a distance. Now when this tuning fork is touched on a table, it causes forced vibration on the table and thereby sound is generated from the table also. Intensity of this sound is relatively high and hence can be heard from a distant location.

Question 20.
What is called resonant vibration ?
Answer:
Resonant vibration: It is a particular case of forced vibration when the frequency of the driving force is equal to the natural frequency of the body. When such condition is fulfilled amplitude of oscillation becomes very high.
Example: A vibration is generated in the air column. When a vibrating tuning fork is placed on the mouth of a pipe filled with air, a shrill sound will be produced. Air being forced vibrated creates this sound.

Question 21.
What is meant by reflection of sound ?
Answer:
Reflection of sound : When sound waves hit on the boundary separating two homogeneous media, a portion of sound changes its direction from the surface of separation and returns to the first medium. This is known as reflection of sound.

Question 22.
State the laws of reflection of sound.
Answer:
Laws of reflection of sound :

• The incident sound, reflected sound and the normal on the surface of separation through the point of incidence remain on the same plane.
• The angle of incidence is equal to the angle of reflection.

Question 23.
What is mach number ?
Answer:
Mach number: The ratio of speed of a body to the speed of sound is called the mach number of the body. If the mach number of a body be greater than 1, then the velocity of the body becomes supersonic velocity.

Question 24.
How does speaking tube operate ?
Answer:
Speaking tube : If we talk at one end of a long tube, it can be heard clearly on the other end. The sound generated at one end does not get scattered. On the contrary, it undergoes several reflections within the tube and finally reaches the other end. In this way, a speaking tube operates.

Question 25.
How does a stethoscope function ?
Answer:
Stethoscope : Doctors use this gadget for chest examination. This is basically a reflecting tube. This gadget consists of two rubber tubes, with a metallic plate at the junction of the tube. The sound of the heart beat reaches from the metallic plate to the ears of the doctor through multiple reflections of the sound within the rubber tubes.

Question 26.
What is echo ? What is the condition for its occurrence ?
Answer:

• Echo : When a sound after reflection from some reflector is again heard separately from the original sound, then this reflected sound is known as an echo.
• Condition : For occurrence of an echo the minimum distance between the source of sound and a reflector of sound producing echo should be arround 16.6 m.

Question 27.
Deduce the minimum distance of a reflector that can produce echo of a transient sound.
Answer:
Minimum distance of the reflector for listening the echo of a transient sound : The sensation of a transient sound remains in our brain is \(\frac{1}{10}\) sec. after it reaches our ear. This period is known as persistence of hearing. If a second sound reaches our brain within this sec. of time, the later one cannot be identified by the brain separately. Obviously a gap of at least sec. \(\frac{1}{10}\) should be there between the original sound and reflected sound so that the brain can recognize them separately.

Now, if the velocity of sound in air be 332 m/sec, \(\frac{1}{10}\) in sec. it travels through 33.2 m. For producing an echo, the total length of path traversed by a sound from the source to the reflector and back should be at least 33.2 m. Hence for hearing echo of a transient sound, the minimum distance of the reflector from the source of sound is half of 33.2 m i.e. 16.6 m.

Question 28.
Give two applications of echo.
Answer:
Applications of echo :

• Determination of velocity of sound in air with the help of stopwatch and a pistol.
• Depth of sea, height of an aeroplane above ground may also be determined with the help of echo.

Question 29.
What is musical sound ?
Answer:
Musical sound : A continuous sound pleasing to the ear and produced by regular and periodic vibrations of a source is known as musical sound.
Example : Sounds generated from different musical instruments like violin, piano, flute etc. are musical sounds.

Question 30.
What is noise ?
Answer:
Noise : A noise is a sound which is discontinuous, unpleasant to the ear and produced by irregular and non-periodic vibrations of a source.
Example : The sounds of moving cars, trains, machines, sound of explosions etc. are the examples of noise.

Question 31.
What do you mean by tone ?
Answer:
Tone : A musical sound having a single frequency is known as tone.
Example : The sound generated from a tuning fork has a unique frequency. Hence the sound generated from a tuning fork is a tone.

Question 32.
What is meant by Note ?
Answer:
Note: A musical sound however generally consists of number of components having different frequencies. Such a sound is known as note.

Question 33.
What is fundamental tone and what is overtone ?
Answer:
Fundamental tone : In a note the tone of lowest frequency is known as fundamental tone.
Overtone : All tones, except fundamental tone, present in a note are known as overtones.

Question 34.
What is harmonics and what is an octave ?
Answer:

• Harmonics : Those overtones whose frequencies are integral multiples of the frequency of the fundamental tone are called harmonics.
• Octave : The particular harmonic whose frequency is double the fundamental frequency is known as the second harmonic or octave of the fundamental tone.

Question 35.
What are the characteristics of musical sound ?
Answer:
Characteristics of musical sound: Musical sound has three important characteristics. These are :

• Intensity
• Pitch and
• Quality or timbre

Question 36.
What is intensity of a musical sound ?
Answer:
Intensity : It means how forcefully or how strongly the sound reaches to a listener. Intensity or loudness of a sound depends on the energy contained per unit volume of the medium through which sound passes.

Question 37.
What are the factors which affect intensity of a musical sound ?
Answer:
The intensity of a musical sound depends upon the following factors :

• Amplitude of the vibration of the source
• Size of the sounding body
• Distance of the observer from the source
• Presence of other bodies
• Density of the medium.

Question 38.
What is pitch ? On what factory pitch of a note depends ?
Answer:

• Pitch: The characteristic of a musical sound by which a sharp or a shrill sound is distinguished from a dull, flat sound of the same intensity is known as its pitch.
• Pitch of a note depends: Pitch of a note depends on its frequency. Greater the frequency, higher will be the pitch. Wavelength being inversely proportional to frequency, the sound of low wavelength has higher pitch and vice versa.

Question 39.
What is quality of a musical sound ?
Answer:
Quality of a musical sound : It is the characteristic of a musical sound which enables us to distinguish one sound from another even though the two sounds may have the same intensity or pitch. Richer the quality, more pleasant is the sound.
Example : If harmonium and violin are played simultaneously, one can easily distinguish between these two even without seeing. This distinction is felt out of the property called quality of sound.

Question 40.
What is sound pollution ?
Answer:
Sound pollution : Any unpleasant and unwanted sound is noise. Sound pollution means creation of discomfort, disturbance and irritation which result to ill effects to mental and physical health.

Question 41.
What are the sources of sound pollution ?
Answer:
Sources of sound pollution :

• The sound of vehicle causes sound pollution.
• The machinery used in industries creates sound of intensity more than tolerance limit and thereby causes sound pollution.
• Loudspeakers, amplifiers, air horn played at top volume are major sources of sound pollution.
• The sound crackers cracked in different functions e.g. Puja ceremony, Marriage ceremony etc. causes sound pollution.

Question 42.
What are the harmful effects of sound pollution ?
Answer:
Harmful effects of noise pollution :

• Sound pollution may cause hinderance in the growth of nervous system of a child in the womb.
• One may become deaf due to sound pollution.
• The sound of high intensity and pitch may cause blood pressure, nervous breakdown, heart disease, loss of memory, loss of concentration etc.

Question 43.
What are the remedial measures of sound pollution ?
Answer:
Remedial measures of sound pollution :

• Factory should be prohibited in residential area.
• Sound resistant measures may be taken in industry.
• Unnecessary use of horn in the vicinity of hospital, school etc should be restricted.
• Airport should be away from residential area.
• Sound pollution awareness programme should be taken up at regular interval.

Question 44.
Why does the sound of explosion occuring in the sun not reach the earth ?
Answer:
Explanation: The continuous explosive sounds occuring in the sun because of conversion of hydrogen to helium by nuclear fusion is not heard from the earth. This is due to the presence of a large space beyond the earth’s atmosphere without any material medium. The sound of explosion cannot transmit to the earth since sound cannot propagate without the help of a material medium.

Question 45.
Why it is not advisable to regulate a watch on hearing the sound of a distant siren ?
Answer:
Explanation: The sound from the siren at a distance takes some time to reach a place. If the person adjusts his watch with the idea that the sound of the siren reaches him just at the time of its production, his watch will be slow by a few seconds that is taken by the sound to reach him.

Question 46.
Why are voices of females or babies more sharp than that of a grown up male person ?
Answer:
Explanation : Vocal cords of females or babies are tender, so, while they speak or sing the cords vibrate with high frequency, for this reason their voices are very sharp. Vocal cords of male persons are usually stiff, so their frequency of vibration is low and hence male voices are generally flat.

Broad answer type questions 

Question 1.
Why sound waves are called elastic waves ?
Answer:
Reason :

• Sound waves require some time to travel from one place to another. Just like on elastic wave.
• Vibration of sources are necessary for the production of elastic waves.
  Sound waves also require vibration of the sources for their production.
• The particles of the medium through which elastic waves pass, are not bodily moved when the waves pass through then. The same thing happens for the sound waves.
• Like all other elastic waves, sound waves require a material medium for their propagation.
• Sound waves like all other elastic waves undergo reflection, refraction and interference.

Question 2.
Describe in brief an experiment which shows that a material medium is necessary for propagation of sound.
Answer:
Experiment to prove
the necessity of material medium for propagation of sound :
Experimental setup: A glass jar is placed in airtight condition on a platform provided with a suction pump. An electric bell kept suspended inside the jar can be operated from outside with the help of a battery.

Experiment : The electric bell is set into operation. Air from inside the jar is gradually drawn out.

Observation : A sound of the bell is heard when the jar is full of air but the sound gradually fades away on withdrawal of air. The sound is again heard clearly when air is re-introduced.

Inference : Since sound from the electric bell is not heard in absence of air within the jar, it proves that sound from a source cannot propagate in absence of a material medium.

Numerical Problems :

Working formula]
(i) υ = vλ (υ = wave velocity,
v = frequency, λ = wavelength)

(ii) s = υ x t (s = Distance,
υ = velocity of sound
t = time)

(iii) υ_t = ν₀ (1 + 0.00 183t)
ν>₀ = velocity of sound at 0°C
υ_t= velocity of sound at t°C)

(iv) Height of an aeroplane above ground (h) = \(\frac{t}{2} \sqrt{v^2-u^2}\)
(υ = velocity of sound
u = velocity of aeroplane
t = time interval of sound and echo)

(v) \(v=\frac{s}{2}\left(\frac{1}{t_1}+\frac{1}{t_2}\right)\)
(v = velocity of sound
s = distance, t₁ initial time t₂ final time)

Problem 1:
The velocity of sound in air is 350 m/s. Frequency of a tuning fork is 700/s. Find the wavelength of the sound generated by the tuning fork.
Answer:
We know,
n = 700sec
λ = ?
y = 350 m/sec.
υ = vλ
Or, λ — \(\frac{v}{v}\)
= \(\frac{350}{700}\)=0.5m

Problem 2:
The frequency of a tuning fork is 440 Hz. If the wave length of the wave is 0.73 m then find the velocity of sound.
Answer:
v = 440 Hz
λ = 0.73m
υ =?
We know,
υ = vλ
or, v = 440 x 0.73
= 321.2 m/s

Problem 3:
A boat approaches a high vertical cliff. When the anchor is dropped, an echo is heard 2s later. How far is the boat from the cliff? (velocity of sound = 332 m/s)
Answer:
As the velocity of sound is 332 m/s so total distance travelled by sound in 2 s is = 2 x 332 = 664 m.
For an echo, the sound must go to the cliff and return through the same distance.
So the distance of the boat from the cliff = \(\frac{664 \mathrm{~m}}{2}=332 \mathrm{~m}\)

Problem 4 :
In measuring the depth of an ocean, it was found that the sound of an explosion and its echo by the bed had a time interval of 20s. between them
Answer:
As the velocity of sound in water = 1436 m/s, so total distance
travelled by the sound in 20s = 20 x 1436 m
The depth of the ocean = \(=\frac{20 \times 1436}{2} \mathrm{~m}\)
= 14360m

Problem 5 :
Find the frequency of a tuning fork whose wave length is 17m.? (velocity of sound in air = 340 m/s)
Answer:
υ= 340m/s
λ = 1.7m
v = ?
We know,
υ = vλ
or \(v=\frac{v}{\lambda}\)
= \(\frac{340}{1.7}\)
= 200 Hz
∴ Frequency of the tuning fork = 200 Hz

Problem 6 :
Two persons A and B are standing 1 km apart in open air. ‘A’ fires a gun and ‘B’ will receive the sound after 3 second of the flash. Calculate the velocity of sound in air.
Answer:
s = 1km = 1000m
t = 3
v = ?
We know,
\(v=\frac{s}{t}\)
or \(v=\frac{1000}{3}\)
∴ velocity of sound in open air = 333.3 m/s

Problem 7.
What should be the minimum distance of the reflector from the source of sound to hear the echo of the word ‘Beautiful’? (velocity of sound = 340 m/s)
Answer:
The word ‘beautiful’ is a trisyllabic one. So to hear it distinctly, one would require \(\left(3 \times \frac{1}{5}\right)\)  s = \(\frac{3}{5}\) = s to pronounce it.
In \(\frac{3}{5}\) sec sound travels \(\left(340 \times \frac{3}{5}\right)\) m = 204m
Thus, the minimum distance of the reflector from the source should be
= \(\frac{204 \mathrm{~m}}{2}\) = 102m

Detailed explanations in West Bengal Board Class 9 Physical Science Book Solutions Chapter 1 Measurement offer valuable context and analysis.

WBBSE Class 9 Physical Science Chapter 1 Question Answer – Measurement

Very short answer type questions

Question 1.
What is a physical quantity ?
Answer:
A physical quantity is any measurable quantity of an object or an event.

Question 2.
For clear understanding what must be present in the result obtained after measuring a physical quantity ?
Answer:
Unit.

Question 3.
By which instrument we to measure the weight of a body ?
Answer:
Spring balance.

Question 4.
Is litre a fundamental unit or a derived unit ?
Answer:
Derived unit.

Question 5.
What is the unit of atomic weight ?
Answer:
No unit.

Question 6.
Is light-year a fundamental or a derived unit ?
Answer:
Fundamental unit.

Question 7.
How many fundamental physical quantities are present in the derived physical quantity momentum ?
Answer:
Three. They are Mass, Length, Time.

Question 8.
Is work done by a force a scalar or a vector quantity ?
Answer:
Scalar quantity.

Question 9.
Which unit should be chosen to measure the distance between two stars ?
Answer:
Light year.

Question 10.
What is the SI unit of temperature ?
Answer:
Kelvin.

Question 11.
Write down a physical quantity which has no unit ?
Answer:
Atomic weight.

Question 12.
What type of time measuring device is used in a race?
Answer:
Stop-watch.

Question 13.
Which physical quantity is measured by a common balance?
Answer:
Mass.

Question 14.
What is the type of unit of velocity ?
Answer:
Derived unit.

Question 15.
Whose unit is millilitre ?
Answer:
Volume.

Question 16.
What is the unit of length in SI system ?
Answer:
Metre.

Question 17.
Name one physical quantity whose unit is formed by using all the three fundamental units.
Answer:
Force.

Question 18.
Which instrument is usually used to measure length ?
Answer:
Ordinary scale.

Question 19.
What is the unit of density in SI system ?
Answer:
kg m³.

Question 20.
What is the unit of volume in CGS system ?
Answer:
cm³

Question 21.
Is unit of area a fundamental unit ?
Answer:
No.

Question 22.
How many seconds are there in a mean solar day ?
Answer:
86,400 seconds.

Question 23.
What must be mentioned in the result obtained after measuring a physical quantity apart from a number?
Answer:
Unit must be mentioned in the result.

Question 24.
Name two physical quantities having same unit ?
Answer:
Speed and velocity.

Question 25.
Why is the temperature 4°C mentioned in defining density of water inCGS system ?
Answer:
Because at 4°C, water has maximum density which is 1 c.c. and water has the mass 1g.

Question 26.
Arrange in ascending order of magnitude : 1 micron, 1 angstrom, 1 fermi.
Answer:
1 fermi < 1 angstrom < 1 micron.

Question 27.
What is the unit of refractive index?
Answer:
No unit.

Question 28.
Write down the SI unit of momentum.
Answer:
kg-m/sec

Question 29.
How many metre is one Fermi ?
Answer:
1 Fermi =10^-15 m.

Question 30.
Give an example of a scalar quantity which is the product of two vector quantities.
Answer:
Work.

Question 31.
What is the dimention of force?
Answer:
[MLT^-2].

Question 32.
Name a physical quantity which has a unit but no dimension.
Answer:
Angle.

Question 33.
Which unit should be chosen to measure distance between two planets ?
Answer:
Light year.

Question 34.
Write down the dimension of density.
Answer:
[ML^-3].

Question 35.
Is the unit of volume a fundamental or a derived unit ?
Answer:
Derived unit.

Question 36.
Write down theCGS unit of pressure.
Answer:
dyne/cm².

Question 37.
What is the SI unit of mass ?
Answer:
Kilogram.

Question 38.
Give the name of two scalar quantities which have same unit.
Answer:
Work and energy. Both have SI unit Joule andCGS unit erg.

Question 39.
What is the mass of 1 ml water at 4°C ?
Answer:
1 g.

Question 40.
The density of Hg is 13.6 g cm³. What is the density of Hg in SI system ?
Answer:
13600 kg m³.

Question 41.
At which temperature water has maximum density ?
Answer:
4°C.

Question 42.
Where is chronometer used ?
Answer:
The mariners use the chronometer for finding out longitude of a plane.

Question 43.
What is the dimension of velocity ?
Answer:
[LT^-1]

Question 44.
What is the dimension of retardation ?
Answer:
[LT^-2]

Question 45.
Which physical quantity has the dimension [MLT^-2] ?
Answer:
Force.

Question 46.
What is the SI unit of Force ?
Answer:
Newton.

Question 47.
Which physical quantity is meåsured by spring balance?
Answer:
Weight.

Question 48.
Give an example of a vector quantity which is derived from only one fundamental unit.
Answer:
Displacement.

Question 49.
The word ‘Science’ has its origin in a Latin word. Name it.
Answer:
Scientia.

Question 50.
The word ‘physics’ comes from a Greek word. What is it ?
Answer:
Physis.

Question 51.
What is measured by astronomical units ?
Answer:
Is is used in measuring astronomical distances.

Question 52.
Is ‘par sec’ a unit of time?
Answer:
No. It is the distance at which an arc of length of 1 AU (Astronomical unit) subtends an angle of one second of an arc.

Question 53.
What is the dimension of area?
Answer:
Dimension : The dimensions of a physical quantity are expressed as the powers to which the fundamental units of mass, length and time are raised to obtain the derived unit of the quantity.

Question 54.
What do we measure with a measuring cylinder?
Answer:
A measuring cylinder is used for measuring the volume of a liquid.

Question 55.
Name the device used in measuring weight of a body.
Answer:
Spring balance.

Question 56.
What does a stop watch measure ?
Answer:
Small time interval is measured by stop watch.

Question 57.
What is the multiplicative factor micro (mu) ?
Answer:
10^-6.

Question 58.
What do we measure with a common balance ?
Answer:
We measure the mass of a body usually with a common balance.

Short Answers type Questions

Question 1.
What is the necessity of measurement of a physical quantity ?
Answer:
Necessity of measurement of a physical quantity.
Measurement of a physical quantity gives a clear idea about largeness or smallness of the quantity. Simple eye estimation does not give any exact size of the physical quantity. For this reason, measurement of a physical quantity is very important.

Question 2.
What is physical quantity?
Answer:
Physical quantity : Any measurable physical entity is known as physical quantity.
e.g. length, mass, time etc.

Question 3.
What is scalar quantity ?
Answer:
Scalar quantity : The physical quantity which has only magnitude but no direction is called scalar quantity.
e.g. length, area, volume, mass etc.

Question 4.
What do you mean by vector quantity?
Answer:
Vector quantity : The physical quantity which has both magnitude and direction is called vector quantity.
e.g. displacement, velocity, force, weight etc.

Question 5.
What is unit ?
Answer:
Unit : Unit is the universally accepted definite amount of a physical quantity taken as a standard for the measurement of the same physical quantity of any amount.

Question 6.
What are fundamental units ?
Answer:
Fundamental units : The units of physical quantities like length, mass and time which do not depend on each other and from which units of other physical quantities may be derived, are called fundamental units.

Question 7.
What are derived units ?
Answer:
Derived units : Those units which are derivable from one or more of the fundamental units are known as derived units.
e.g. units of acceleration, force, speed, momentum etc. are derived units.

Question 8.
Has every physical quantity a unit ?
Answer:
No, there are some physical quantities which are measured by the ratio of two identical quantities.
e.g. atomic weight, specific heat, specific gravity etc.
These physical quantities have no units, they are purely numerical numbers.

Question 9.
What are the characteristics of fundamental units ?
Answer:
Characteristics of fundamental units :

1. They do not depend on each other.
2. They can form the units of other physical quantities.
3. They are only three in numbers.

Question 10.
What are the types of different system of units ?
Answer:
Different system of units : At present two different system of units are used in science throughout the world.
(a) CGS or Metric system.
(b) SI or international systems of units (1960).

Question 11.
What isCGS system ?
Answer:
CGS or French or Metric system : This system was originated in France but now it is used in the scientific measurements and is widely used throughout the world including India. From the initial letters of the words centimetre, gram and second, this system is calledCGS system. This is a decimal system.

Question 12.
What is SI unit ?
Answer:
SI or International System of units : In 1960, an international system of units of measurement known as SI system was recommended by the GeneralConference on Weights and Measures in order to have a consistent system of units and to simplify communications among the scientists.

Question 13.
Define metre.
Answer:
Metre : The distance between the two marks made on a platinum-iridium (90: 10) bar maintained at 0°C temperature preserved at International Bureau of Weights and Measures at Sevres near Paris considered as one metre (symbol : m).

Question 14.
What is the modern concept of metre ?
Answer:
Modern concept of metre (October, 1983) :
The distance travelled by light in \(\frac{1}{3 \times 10^8}\) sec. in vacuum is called 1 metre.

Question 15.
State different smaller units of length in SI system.
Answer:
Smaller units of length in SI system :

1. Femtometre or Fermi (=10^-15 m)(fm)
2. Picometre (=10^-12 m)(pm)
3. X-ray unit (=10^-13 m)(Xu)
4. Angstrom (=10^-10 m)(A°A)
5. Nanometre (=10^-10 m)(nm)
6. Micrometre or micron (=10^-6 m)
7. Centimetre (=10^-2 m)(cm)
8. Decimetre (=10^-1 m)(dm)

Question 16.
What are the bigger units of length ?
Answer:
Bigger units of length :
(i) Astronomical unit (AU): The average distance between the Earth and the Sun.
1 AU = 14.95 × 10⁸ km
(ii) Light year : The distance that light wave travels in year in vacuum.
1 light year = 9.46 × 10¹² km
(iii) Persec : The biggest unit for the measurement of distance. 1 persec = 3.26 light year = 30.84 × 10¹² km.

Question 17.
What do you mean by mass ?
Answer:
Mass : Mass of a body is the quantity of matter contained in it.

Question 18.
State the bigger units of mass.
Answer:
Bigger units of mass :

1. Quintal (= 100 kg)
2. Metric ton or tonne (= 1000 kg = 10 Quintal)
3. CSL (= 1.4 × mass of the Sun)

Question 19.
State the smaller units of mass.
Answer:
Smaller units of mass :

(i) amu(= 1.6603 × 10^-24g)
(ii) 1 carat = 200 mg

Question 20.
What is density ? State itsCGS and SI units.
Answer:
Density : Density of the material of a body is the quantity of its mass per unit volume.
Unit of density inCGS system : g cm^-3
Unit of density in SI system : kg m^-3

Question 21.
What is Solar day?
Answer:
Solar day : The interval of time between two consecutive apparent transits of the Sun across the meridian at any place is called a Solar day.

Question 22.
What do you mean by mean Solar day ?
Answer:
Mean Solar day : The length of the Solar day varies from day to day owing to various reasons and the mean value of the actual Solar days averaged over a full year is called the mean Solar day.

Question 23.
What is the definition of second in SI system ?
Answer:
Definition of second in SI system : The time taken for the number of vibrations 9,192,631,770 of a radioactive atom Cs¹³³ in standard magnetic field is called one second.

Question 24.
What do you mean by volume?
Answer:
Volume : It is defined to be the space occupied by a substance. Solids have three dimensions i.e. length, breadth and height.

Question 25.
What is litre?
Answer:
Litre : Volume of 1 kg of pure water at 4°C or 277 K is called a litre.

Question 26.
What are the advantages of metric system ?
Answer:
Advantages of metric system :

1. In metric system, multiples and sub-multiples of the units of length and mass are always ten times the preceding ones.
2. In metric system, units of length, mass and volume are related by same relation.
3. In metric system, the same prefixes (such as milli, centi, deci etc.) are used in the units of length and mass.

Question 27.
What is the definition of dimension ?
Answer:
Definition of dimension : Dimensions of a derived unit are the powers to which the fundamental units of mass, length and time must be raised to present that unit.

Question 28.
What is the definition of dimensional expression ?
Answer:
Definition of dimensional expression : Dimensional expression is a product or quotient of the symbols of fundamental physical quantities, involved in a derived physical quantity raised to appropriate powers.
e.g. Dimensional expression of force : [MLT^-2].

Question 29.
State physical quantities without dimension.
Answer:
Physical quantities without dimension : A physical quantity is expressed as a ratio between two physical quantities of same unit becomes a number only, which will not have dimension.
e.g. Mechanical advantage of a machine, specific gravity, refractive index etc. are dimensionless. Again, angle although has unit (radian), it has no dimension.

Question 30.
What is the function of ordinary scale ?
Answer:
Function of ordinary scale : We generally use ordinary scale for the measurement of length.

Question 31.
How can you measure the length of a curved line ?
Answer:
Measurement of the length of a curved line: If the length of a curved line is to be measured with the help of a scale, we make use of a thread and place it along the curved line and measure the length of the straightened thread with the help of a scale.

Question 32.
Why scales are made usually with wood or plastic ?
Answer:
Scales are made
usually with wood or plastic: In making an ordinary scale wood or plastic is usually used instead of metal with the change in atmospheric temperature metal scales change in length. A metal scale gives correct readings only at a temperature at which it has been graduated. At any other temperatures it would give incorrect measurements. But in the case of wood or plastic these changes are negligible. So the scales are made usually with wood or plastics.

Question 33.
What is common balance?
Answer:
Common balance : In the laboratory we measure the mass of a body with a common balance. The weighing balance used in our daily life is simple version of this common balance.

Question 34.
What is the working principle of measurement of mass ?
Answer:
Working principle of measurement of mass : Actually we find the mass of the body by comparing its mass with some standard weights. Generally the measurable object as kept on the left pan of the balance and the standard weights are placed on the right pan. When the balance beam is horizontal, then
Mass of the object = Mass of the Standard Weights

Question 35.
What are the requisites of a good balance?
Answer:
Requisites of a good balance :

1. The balance must be true, i.e. the balance beam should be horizontal with no loads or with equal loads on the pans.
2. The balance must be sensitive.
3. The balance must be stable i.e. the balance beam must came quickly to its equilibrium position once it is displaced.
4. The balance must be rigid i.e. all the parts of the balance must. be strongly built.

Question 36.
What is a sensitive balance ? What are the conditions to be a sensitive balance?
Answer:
Sensitive balance : A balance is said to be sensitive when even for slight difference in weights on the two pans, the beam should be tilted from its horizontal position.
Conditions for balance to be sensitive :
(i) The balance beam should be light with long arms.
(ii) The centre of gravity of the beam should be near the fulcrum.

Question 37.
What is spring balance?
Answer:
Spring balance: With the help of this instrument weight of a body can be measured.

Question 38.
What is the working principle of measurement of weight ?
Answer:
Working principle of measurement of weight : The spring balance should be kept vertical and the pointer should be coincide with the ‘0’ mark of the scale. When a weight is suspended from the hook, the spring elongates, elongation being proportional to the weight. So, the pointer attached to the spring moves over the graduated scale. By noting its position against the scale, we can directly measure the weight of a body.

Question 39.
What is measuring cylinder ?
Answer:
Measuring cylinder: The instrument by which the volume of a liquid is measured is known as measuring cylinder.

Question 40.
What points should be noted during measuring the volume of liquid?
Answer:
Points should be noted :
(i) The volume of a liquid cannot be measured by measuring cylinder which reacts with glass.
(ii) The volume of a liquid cannot be measured by cylinder which is very much volatile.

Question 41.
How can you measure the density of an irregularly shaped body by using common balance and measuring cylinder ?
Answer:
Density : Density of a substance is defined as mass per unit volume of the substance.
If M be the mass of the substance, V the volume, then the density D is given by D = MV
Mass of the irregularly shaped body is determined by a common balance and volume is measured by a measuring cylinder. From equation (1) density of the body can be determined.

Question 42.
How will you determine the volume of a solid by a measuring cylinder?
Answer:
Determination of the volume of a solid by a measuring cylinder: To find the volume of the solid, some liquid in which the solid sinks but does not dissolve is taken in a dry measuring cylinder. The reading of the upper meniscus of the liquid in the cylinder is noted, let it be V₁ ml . The solid substance tied with a waxed thread is now slowly immersed in the liquid. Let the reading of the upper meniscus of the liquid in a measuring cylinder be V₂ ml. So, the volume of the given solid is (V₂-V₁) ml.

Question 43.
What precautions should be taken while determining volume and density of a solid body with the help of a common balance?
Answer:
Precautions:

1. The body must sink completely in the liquid taken in the measuring cylinder.
2. The body must not react chemically with the liquid and also it must not dissolve in the liquid.
3. While dipping the body in the liquid taken in measuring cylinder, it should be done carefully so that no liquid splashes out.

Question 44.
Is density of a material dependent on its mass or volume?
Answer:
Density of a substance is independent of its mass or volume. If the mass of a substance is increased or decreased, its volume correspondingly increases or decreases proportionately and vice versa. So, density, the ratio of mass to volume remains unaltered.

Question 45.
Why is temperature kept at 4°C is measuring the volume of a liquid in litre unit ?
Answer:
Density of pure water is maximum at 4°C and it varies with the change of temperature and so also the volume. Hence, temperature of 4°C is specified in litre unit.

Question 46.
Why one does not express his age in second?
Answer:
A person does not express his age in seconds, because with such a small unit of time the number expressing his age will be very large that gives no clear idea about the age. Above all, in calculating age in seconds and then expressing it with a large number, some more seconds will pass off which do not come into the calculation. So, the correct age of one cannot be expressed in seconds.

 Broad answer type Questions

Question 1.
Distinguish between scalar and vector quantities.
Answer:
Difference between scalar and vector quantities :

Scalar guantity	Vector quantity
(i) Scalar quantities have only magnitude and no direction.	(i) Vector quantities have both magnitude and direction.
(ii) Scalar quantities change due to change of magnitude only.	(ii) Vector quantities change due to change of magnitude or direction or both.
(iii) So far as addition, subtraction, multiplication etc. are concerned, scalar quantities obey algebraic laws.	(iii) So far as addition, subtraction multiplication etc. are concerned, vector quantities do not obey algebraic laws.

Question 2.
Write down the names and symbols of the fundamental units in SI system.
Answer:
Various fundamental physical quantities in SI system :

Question 3.
What are the advantages of metric system ?
Answer:
Advantages of metric system :
(i) In metric system, multiples and sub-multiples of the units of length and mass are always ten times the preceding ones. Thus the system is known as decimal system.In this system conversion of different multiples and sub-multiples of the units could be done by shifting the decimal point to the right or left.
(ii) In metric system, units of length mass and volume are related by simple relation.
(iii) In metric system, the same prefixes (such as milli, centi, deci etc.) are used in the units of length and mass

Question 4.
Why is temperature mentioned in the unit of length but not in the unit of mass ?
Answer:
The length is measured by a scale made of metals, plastic, wood or Gutta-percha etc. The length of these substances vary with difference of temperature. So in determining the unit of length temperature is to be specified to get the exact length. On the other hand mass being on intrinsic property of matter it does not vary with the change of temperature. So it is not necessary to specify the temperature.

Question 5.
How can you measure the exact mass of a solid by a common batance with unequal arm length ?
Answer:
Suppose the length of left and right arm of the balance are l₁ and l₂ respectively.
Now, keeping the solid with a mass of in at the right hand pan it is counterpoised with a mass w₁ at the left hand pan.
Now, w₁ × l₁ = m × l₂
or, \(\frac{l_1}{l_2}=\frac{m}{w_1}\) ….. …. (i)

Again, the solid of mass ‘m’ is kept at the left hand pan and supposed it is counterpoised with a load of mass w₂ at the right hand pan.

Question 6.
How can you measure the diameter of a piece of hair or thread?
Answer:
Measurement the diameter of a piece of hair or thread : To find diameter of a piece of hair or thread, a long piece of hair or thread is taken. The piece is then coiled over the millimetre marks on the scale. The coiling should be such that each turn remains in close contact of its adjacent one. Thus the added diametre of the segments of hair or thread in all the turns cover a few millimetre of the scale which is noted. Now dividing the length covered by the turns of hair or thread on the scale by the number of turns, diameter of the hair or thread is determined.

Question 7.
In theasuring certain length with a ruier why different portions of the ruier are made co-incident with the two ends of the given length ?
Answer:
As the graduation marks on the scale may not be uniformly spaced, due to manufacturing defects, several portions of the scale should be used i.e. the left end of the line may be made co-incident with different arbitrarily chosen marks of the scale like, 43 cm mark, 5.1 cm mark, 7.2 cm mark etc. The average of the several readings obtained after the above mentioned operations gives the required length of the line almost correctly.

Question 8.
How can you find the radius of a drop of a liquid ?
Answer:
Decermination of the radius of a drop of a hiquid: In order to find the radius of a drop of a liquid, a large number, say 200 drops of the liquid are taken in a dry measuring cylinder of small diameter. The drops of the liquid are taken with the help of a burette. The volume of the liquid is observed from the measuring cylinder. Now, it is divided with the number of drops of liquid taken when the volume of one drop is determined, then v ml = \(\frac{4}{3}\) πr₃, where π = 3.14.
So, the radius of the drop of liquid is determined.

Numerical Problems

Working formula :

(i) Volume of a rectangle solid = length × breadth × height
= l × b × h
(ii) Volume of a cube =(length)₃=l₃
(iii) Volume of a sphere = \(\frac{4}{3}\) π(radius )₃ = \(\frac{4}{3}\) πr₃
(iv) Volume of a cone = \(\frac{1}{3}\) π × (radius of base)² × perpendicular height
= \(\frac{1}{3}\) πr² h(π = \(\frac{22}{7}\))
(v) Volume of a right circular cylinder =πr² h
(vi) Density of a substance (D) = \(\frac{\text { Mass of the substance }(M)}{\text { Volume of the substance }(V)}\)

Example 1 : The mass of a proton is 1.67 × 10-27 kg. How many protons would be required to make 1 kg ?
Answer:

Example 2: The radius of an atom is abon: 1 A while that of the nucleus is about 1 fermi. How does the volume of the atom compared with that of the nucleus of the atom:
Answer:
1A° = 10^-10 m, 1 fermi = 10^-15 m
So, from the problem we get,

Therefore, volume of the atom is 10¹⁵ times greater than that of the nucleus.
Example 3 : Light of a certain colour is composed of a train of waves, each of 0.3048 micron long. How mans of the are are there in a metre?
Answer:
1 micron =10^-6 m
∴ Number of waves

Example 4 : Mankind has existed for about 106 years, whereas the universe is about 1010 years old. If the age of the universe is taken to be one day, for how many seconds has mankind existed?
Answer:
From the problem we get,

10¹⁰ years =24 × 60 × 60 sec.

Example 5 : Mass of a piece of gold in air is 193 g. In a measuring cylinder there is 50 cm 3 of water. When the piece of gold is immersed in water in the measuring cylinder, the reading of the volume of water is found to be 60 cm 3. What is the density of gold?
Answer:
From the problem we get, Volume of the piece of gold =(60-50) cm³=10 cm³

Example 6: If the mass and volume of a piece of iron be 760 g and 100 cm³, then what would be its density?
Answer:
Density of iron = \(\frac{\text { mass of iron }}{\text { volume of iron }}\)
= \(\frac{760 \mathrm{~g}}{100 \mathrm{~cm}^3}\) = 7.6 g/cm³

Example 7 : The volume of a can is 100 ml and it weighs 20 g. It is then filled fully by a liquid and weighs 180 g. Find the density of the liquid.
Answer: Volume of the liquid (v) = 100 ml
Mass of the liquid (M) = (180-20) g = 160 g

Example 8: The density of a liquid is 1.2 g / cm³. What will be the mass of 100 cm³ of the liquid?
Answer: Volume of the liquid =100 cm³
Density of the liquid =1.2 g / cm³
We know,

Mass of liquid =volume of the liquid × density of the liquid
= (100 × 1.2)g = 120g

Example 9 : The density of silver in CGS unit is 10.5 g / cm³. What will be the density of silver in SI unit?
Answer: From the problem we get, density of silver in CGS unit =10.5 g / cm³
So, the density of silver in SI unit
= 10.5 × 1000 kg / m³
= 10500 kg / m³

Example 10: The radius of a solid sphere is 10 cm. The density of its matter is 8 g / cm 3. What is the mass of the sphere?
Answer:
We know,
volume of the sphere V = \(\frac{4}{3}\) πr³(r= radius of the sphere)
∴ \(\frac{4}{3}\) × \(\frac{22}{7}\) × (10)³ cm³ ; r = 10cm
Density of its matter = 8 g/cm³
So, mass of sphere = volume × density
= \(\frac{4}{3}\) × \(\frac{22}{7}\) ×(10)³ × 8g=33.51 kg

Example 11.
Mass of a piece of solid substance is 20.52 g. When the piece is immersed in water its mass becomes 12.48 g. What will be its volume and density?
Answer:
Mass of displaced water by the body =(20.52-12.48) g=8.04 g
Volume of displaced water = \(\frac{8 \cdot 04}{1 \mathrm{~g} / \mathrm{cc}}\) = 8.04 c.c.
So, the volume of the solid substance = 8.04 c.c.
Density = \(\frac{20 \cdot 52}{8 \cdot 04}\) g / c.c. =2.55 g / c.c.

Example 12.
Find the dimension of force.
Answer:

Example 13.
Specific gravity is the ratio of two densities. Show that it has no dimension.
Answer:
Specific gravity of a substance

So, specific gravity is dimensionless.

Example 14.
Kinetic energy is given by \(\frac{1}{2}\) mv 2 and potential energy by mgh. Show that both of them have same dimensions.
Answer:
Kinetic energy =\(\frac{1}{2}\) mv²
= [M] ×[LT^-1]^-2=[ML² T^-2]
Potential energy =mgh=[M] ×[LT^-2] ×[L]
= [ML² T^-2]
So, kinetic and potential energies have same dimensions.

Example 15.
Find the dimension of power.
Answer:

Example 16.
In CGS system density of water is 1 g / cc. Find the density of water in SI unit.
Answer:
Density of water =1 g / cc
= 1 g / 1 cm³

∴ Density of water in SI unit is 1000 kgm^-3.

Example 17 :
xpress a light year in megametre
Answer:
Light year is the distance travelled by the light in one year at the speed 3 × 10⁸ m / s.
One megametre =10⁶ m
∴ Distance travelled by light in one year (365 days)

= 94608 × 10⁵ Mm