WBBSE Class 7 Science Solutions Chapter 1.3 Magnet

Detailed explanations in West Bengal Board Class 7 Science Book Solutions Chapter 1.3 Magnet offer valuable context and analysis.

WBBSE Class 7 Science Chapter 1.3 Question Answer – Magnet

(Page no. 38)

Now take the bar magnet near each of these obfects and note which of these are being attracted by the magnet.
Answer:

Class 7 Science Chapter 1.3 Question Answer West Bengal Board –Magnet

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

Question 1.
A magnetic substance-
i) plastic
ii) wood
iii) iron
iv) stone
Answer:
iii) iron

Question 2.
A non-magnetic substance-
i) plastic
ii) cobalt
iii) iron
iv) nickel
Answer:
i) plastic

Question 3.
Magnetities are called-
i) natural magnets
ii) artificial magnets
iii) man-made magnets
Answer:
i) natural magnets

Question 4.
The attractive power of a bar magnet is strongest at its-
i) north pole
ii) midpoint
iii) both poles
Answer:
iii) both poles

Question 5.
Two opposite poles of magnets-
i) repulse
ii) attract
iii) remain neutral
Answer:
ii) attract

Question 6.
Which is incorrect-
i) induction occurs before attraction
ii) like poles repel each other
iii) a magnet has directional property
iv) single magnetic pole can exist
Answer:
iv) single magnetic pole can exist

Question 7.
Heating destroys magnetic property of-
i) ATM card
ii) hard disk of a computer
iii) loudspeaker
iv) all of these
Answer:
iv) all of these

Question 8.
There is a magnetite in pigeon’s body between-
i) neck and head
ii) neck and breast
iii) skull and brain
iv) between two wings
Answer:
iii) skull and brain

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

1. About 2500 years ago a shepherd named _____ discovered magnet.
Answer:
Magnes

2. Material that are not attracted by a magnet are called _____ substances.
Answer:
non-magnetic.

3. Materials that are attracted by a magnet are called _______ substances.
Answer:
magnetic

4. ______ is a non-magnetic substance.
Answer:
Rubber

5. One end of a magnet is north-pole and another end is ______.
Answer:
south-pole

6. Magnetites are called ______.
Answer:
natural magnets

7. A _____ has the property to attract iron.
Answer:
magnet

8. Unlike poles of magnets _____, whereas like poles _____ each other.
Answer:
attract, repel

9. The earth itself behaves like a huge _______.
Answer:
magnet

10. ______ are used in dynamo of a bicycle.
Answer:
magnets

11. _____ birds and ______ travel following the lines of force of earth’s magnetic field.
Answer:
Migratory, turtles.

12. There is a small black magnetic substance between the skull and brain of ________.
Answer:
pigeons

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

1. Electromagnets are used in electric calling bell.
2. A blade is attracted by magnet.
3. A rubber is attracted by magnet.
4. Cobalt is not attracted by magnet.
5. North poles of two magnets attı act each other.
6. A magnet suspended freely always comes to rest only north-south direction.
7. Only one pole exists in a magnet.
8. Magnetic poles always exist in pairs.
9. The earth itself behaves like a huge magnet.
10. Magnets are not used in loudspeakers.
11. Magnetic trips are used in ATM cards and credit cards.
12. Attraction occures before induction.
Answer:
1. true
2. true
3. false
4. false
5. false
6. true
7. false
8. true
9. true
10. false
11. true
12. false

a. Match the column A with column B.

Column A	Column B
a) A magnet has	i) in electric meters
b) A magnet attracts	ii) before attraction
c) Heating destroys	iii) can not exist
d) Magnets are used	iv) two opposite poles
e) An animal can	v) kept near loudspeakers
f) Induction occurs	vi) magnetized strip of steel
g) Single magnetic poles	vii) magnetic materials
h) Strong magnet should not	viii) two types
i) Magnetic needle is small	ix) magnetic property
j) Magnets are of	x) recognize earth’s magnetic field

Answer:
a) A magnet has two opposite poles.
b) A magnet attracts magnetic materials.
c) Heating destroys magnetic property.
d) Magnets are used in electric meters.
e) An animal can recognize earth’s magnetic field.
f) Induction occurs before attraction.
g) Single magnetic poles can not exist.
h) Strong magnet should not kept near loudspeakers.
i) Magnetic needle is small magnetized strip of steel.
j) Magnets are of two types.

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

Question 1.
What type of magnet is magnetite?
Answer:
Magnetite is a natural magnet.

Question 2.
Who and how many years ago discovered magnet?
Answer:
About 2500 years ago a shepherd named Magnes discovered magnet.

Question 3.
What are Magnetic substances? Give example.
Answer:
Materials that are attracted by a magnet are Magnetic subtances. Example-iron, nickel, cobalt.

Question 3.
What are Magnetic substances?
Answer:
Materials that are not attracted by a magnet are called non-magnetic substances. Example-plastic, rubber, wool.

Question 5.
What type of magnet is produced if electricity is passed through iron?
Answer:
Electro-magnet is produced.

Question 6.
Name two things where electromagnets are used.
Answer:
Electromagnets are used in electric calling bell and electric motors.

Question 7.
What are Artificial Magnets?
Answer:
Artificial Magnets are prepared by magnetising some suitable magnetic subtances.

Question 8.
What is the directive property of magnet?
Answer:
The property by which a floating or hung magnet is able to rotate freeely orienting itself North-South is called directive property of magnet.

Question 9.
What is bar magnet?
Answer:
A bar magnet is a magnetised sample of steel having a rectangular paralleopipod shape.

Question 10.
What are non-magnetic substances?
Answer:
Materials that are not attracted by a magnet are called non-magnetic substances. Example – plastic, wood, paper.

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

Question 1.
What are Natural Magnets or Magneite?
Answer:
Magnets which are available in nature are Natural Magnets or Magnetite. However, these are not commercially available. Such materials are available in specific areas only

Question 2.
Where do you think the attracting power of the magnet is (i) the strongest, (ii) the weakest.
Answer:
i) The attracting power of a bar magnet is strongest at its both ends. These regions are called the ‘pole of the magner’.
ii) Attracting power of a magnet is practically zero at its mid point. The region is called the ‘neutral zone’ of a magnet.

Question 3.
What is magnetic length? How it can be calculated?
Answer:
The distance between the north and the south poles of a magnet is called magnetic length of a bar fisagnet. This length is about 0.86 times the geometric length of the magnet.
So magnetic : ingth = 0.86 × geometric lentgth of the magnet.

Question 4.
What is magnetic axis?
Answer:
The line segments obtained by joining the geometric poles of a magnet, is called the magnetic axis.

Question 5.
Mention some roles of Magnetic field on the Physiology of Animals.
Answer:
The effect of magnetic field on some organisms had been studied by scientists. Beginning their journey from their native habitats, migratory birds and animals reach their winter habitats by following the lines of force of earth magnetic field.

Question 6.
What is magnetic field?
Answer:
The region around a magnet where its attractive and repulsive effects are felt, is called the magnetic field of the bar magnet.

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

Question 1.
What is magnetic induction?
Answer:
When a magnet attracts a magnetic material, the material is magnetised by induction, then it becorves a temporary magnet and under the influence of the bar magnet it can attract other magnetic materials. This phenomenon is known as ‘magnetic induction’.

Question 2.
Write down the properties of a magnet.
Answer:
The properties of a magnet are –
a) A magnet attracts magnetic materials.
b) A magnet has directive property.
c) Like poles repel each other, unlike poles attract each other.
d) A magnet can induce magnetism in a magnetic substance.
e) Attraction follows induction.
f) A magnet always has two opposite poles.
g) Single magnetic poles cannot exist.

Question 3.
Is the Earth a magnet?
Answer:
The earth itself behaves like a huge bar magnet. We have learnt that the unlike poles attract each other. If a bar magnet is suspended from a support and allowed to rotate freely, it rests itself in North-South direction. This is because the magnetic North Pole of the earth is near the geographical South Pole, whereas the magnetic south pole is near the geographical North Pole.

Question 4.
What the North Pole and South Pole of a magnet actually means?
Answer:
Actually the so-called North and South Poles of a magnet should properly be called ‘Nouth-seeking pole’ and ‘South-seeking pole’ respectively. However, in our everyday ‘North pole’ and ‘South pole’ respectively.

Question 5.
What are Electro-magnets?
Answer:
When an iron bar is wrapped with an electric wire and electricity is passed through it. it behaves like a magnet. This type of magnet is called electromagnet.

Question 6.
Write down some uses of magnet.
Answer:
Uses of magnet –

1. Crews of ship use marine conpass that help them navigate their vessel.
2. The spools of audio and video cassettes are coated with a magnetic substance.
3. Magnetic strips are used in ATM cards and credit cards.
4. The hard disks of computers contains plastic disk coated with a magnetised material.
5. Many toys employ magnets.
6. Doctors use a special type of magnet to extract finer dust of iron accidentally fallen in someone’s eyes.
7. Magnets are used in loudspeakers.
8. Magnets are used in dynamo of a cycle.
9. Magnets are used in electric meters.
10. The door of refrigerators have magnets attached with them.

Question 7.
What precautions should be used in handling magnets?
Answer:
Instruments in which magnets are used must be handled with care. Such instruments must not be heated. Heating destroys magnetic property. The magnetic strips of two ATM cards kept together must not face each other. No strong magnet should not be kept near loudspeakers, TV, radio or hard disk of a computer.

Question 8.
How Aurora is formed?
Answer:
A special kind of rays called cosmic rays, enter the earth’s atmosphere. The charged particles in cosmic rays interact with the earth’s magnetic field and two radiation zones (Van Allen radiation belt) are formed. Auroral is also fromed. Living organisms utilise this aurora for their survival.

Question 9.
How can an animal recognize earth’s magnetic field?
Answer:
There is a black structure between the skull and brain of pigeons. This contains magnetic substance, called magnetite. In the dusk, pigeons return to their nests without mistake. However. if small magnets are fixed to their head. they fail to do so and fly in wrong direction. Magnetites have been found in some bees and animals.