Detailed explanations in West Bengal Board Class 7 Science Book Solutions Chapter 1.4 Electricity offer valuable context and analysis.
WBBSE Class 7 Science Chapter 1.4 Question Answer – Electricity
(Page no. 55)
Complete the table.
Answer:
Class 7 Science Chapter 1.4 Question Answer West Bengal Board –Electricity
Multiple Choice Questions & Answers : (1 mark for each question)
Question 1.
The fish that can produce electricity in their body-
i) electric eel fish
ii) cat fish
iii) trout fish
Answer:
i) electric eel fish
Question 2.
Inside electric iron there is wire made of-
i) Copper
ii) Silver
iii) Nichrome
Answer:
iii) Nichrome.
Question 3.
Filament is made up of –
i) Aluminium
ii) Tungsten
iii) Nickel
Answer:
ii) Tungsten
Question 4.
At a relatively low temperature fuse wire-
i) melts
ii) remains it is
iii) changes slightly
Answer:
i) melts
Question 5.
A combination of number of cells forms-
i) dry cell
ii) filament
iii) battery
Answer:
iii) Battery.
Question 6.
Positive terminal is marked by the sign-
i) +
ii) –
iii) ×
Answer:
i) +
Question 7.
Good conductor of electricity is-
i) wood
ii) plastic
iii) copper
iv) paper
Answer:
iii) copper.
Question 8.
In the cell chemical energy is converted into-
i) mechanical energy
ii) chemical energy
iii) magnetic energy
iv) electrical energy
Answer:
iv) electrical energy
Question 9.
Other name of disposal cell is-
i) secondary cell
ii) primary cell
iii) button cell
iv) terminal
Answer:
ii) primary cell
Question 10.
If the circuit is not disconnected any where then that circuit is called-
i) closed circuit
ii) open circuit
iii) blocked circuit
Answer:
i) closed circuit
Question 11.
A bad conductor of electricity-
i) copper
ii) iron
iii) China clay
iv) silver
Answer:
iii) China clay
Question 12.
In electric calling bell there is-
i) static electricity
ii) electromagnet
iii) natural magnet
Answer:
ii) electromagnet.
Question 13.
In solar calculator the energy of light from the sun is transformed into-
i) electrical energy
ii) magnetic energy
iii) electromagnetic energy
Answer:
i) electrical energy
Question 14.
The sfficiency of solar panel is-
i) high
ii) very high
iii) low
iv) very low
Answer:
iv) very low
Fill in the blanks : (1 mark for each question)
1. ________ is formed by combination of a number of cells.
Answer:
Battery.
2. ________ is called ‘primary cell’ or ‘disposable cell’.
Answer:
Dry cell.
3. There are ________ substances in the cell of torch.
Answer:
chemical.
4. The inner part of the bulbs which glows when switch is on, is called ________.
Answer:
filament.
5. Plastic, china clay, wood ete are all ________ of electricity.
Answer:
bad conductor.
6. In electric calling bell ________ is used.
Answer:
electromagnet.
7. In electric iron there is ________ wire.
Answer:
Nichrome.
8. The filament of bulb is made of ________ metal.
Answer:
tungsten.
9. ________ wire is used for the safety of any electrical circuit.
Answer:
Fuse.
10. In telephone ________ is used.
Answer:
electromagnet.
11. The body fluids of all organisms contain various charged ________.
Answer:
particles.
12. The positive end of LED is ________ than the negative end.
Answer:
larger.
State whether True or False : (1 mark for each question)
1. Dry cells are used in torch.
2. There are physical substances in the cell of a torch.
3. Battery is formed by combination of a number of cells.
4. If the number of turns of wire increases then the magnetic strength of electromagnet also increases.
5. If the quantity of electricity increases, the strength of the electromagnet decreases.
6. Fuse wire is used for the safety of any electrical circuit.
7. The filament of bulb is made of Aluminium metal.
8. The bodies of all living organisms consist of molecules and atom.
9. There is a system to generate electricity in bodies of Hilsa, Trout fish.
10. Brain consists of numerous nerve cells.
Answer:
1. true
2. false
3. true
4. true
5. false
6. true
7. false
8. true
9. false
10. false
Match the column A with column B.
| Column A | Column B |
| a) Electro magnet is used | i) electronic wristwatch |
| b) The number of cells increases | ii) has two terminals |
| c) Electricity can not pass | iii) in solar calculator |
| d) Button cell is used in | iv) relatively low tremperature |
| e) A cell | v) through plastic goods |
| f) Primary cell is known as | vi) inside the electric iron |
| g) Solar panel supplies electricity | vii) to make motor |
| h) Fuse wire melts at a | viii) is made of tungsten |
| i) Nicrome wire is used | ix) strength of electreomagnet increases |
| j) The filament of a bulb | x) disposable cell |
Answer:
a) Electro magnet is used to make motor.
b) The number of cells increases strength of electreomagnet increases
c) Electricity can not pass through plastic goods.
d) Button cell is used in electronic wristwatch.
e) A cell has two terminals.
f) Primary cell is known as disposable cell.
g) Solar panel supplies electricity in solar calculator.
h) Fuse wire melts at a relatively low tremperature.
i) Nicrome wire is used inside the electric iron.
j) The filament of a bulb is made of tungsten.
Short Questions & Answers : (1,2 marks for each question)
Question 1.
What is ‘primary cell’ or ‘disposable cell’?
Answer:
There are chemical substances in the cell of torch. In the cell chemical energy is converted into electrical energy. This cell is called ‘pimary cell’ or ‘disposable cell’.
Question 2.
How many terminals are there in a ‘cell’?
Answer:
A ‘cell’ has two terminals-a) ‘Metallic cap’ terminal or (+) signed terminal. b) ‘Metallic disk’ terminal or (-) signed terminal.
Question 3.
Do you know any device which can be run by solar energy?
Answer:
Solar cooker. solar table fan, solar tubelight. solar street light etc. are run by solar energy.
Question 4.
What is Button cell?
Answer:
The cell present in the electronics wrist watch looks like a button. This is called Button cell.
Question 5.
What is secondary cell?
Answer:
There are six or more than that cells in the powerful battery of a car. Such type of cell is called secondary cell.
Question 6.
What is filament? Explain how it is connected inside a bulb?
Answer:
The inner part of the bulb which glows when switch is on, is called filament.
Filament is connected between two thick metallic wires. One of that two thick wires is connected with the positive (+ signed) terminal of the cell and other is connected with the negative (- signed) terminal of the cell.
Question 7.
What is circuit?
Answer:
To make the bulb glow, both the terminals of the bulb are connected with the opposite terminals of the cell. This arrangement is called circuit.
Question 8.
What is open and closed circuit?
Answer:
An open circuit is one where the continuity has been broken by an interruption in the path for current to flow. A closed circuit is one that is complete, with good continuity throughout.
Question 9.
Which subtances are called ‘good conductors of electricity’?
Answer:
The subtances through which electricity can pass easily are called good conductor of electricity. As example – Copper, Iron, Aluminium.
Question 10.
Which substances are called ‘bad conductors of electricity’ or insulators?
Answer:
The subtances through which electricity cannot pass are called bad conductors of electricity or insulators. As example-plastic, wood, glass.
Question 11.
What is electromagnet?
Answer:
If wire is bound around a magnetic substance (Iron, Nickel, Cobalt) and electricity is passed through it, the magnetic substance transforms into a magnet. This type of magnet is called electromagnet. When flow of electricity is stopped, it loses its magnetic property.
Question 12.
How the strength of a electromagnet could be increased?
Answer:
(a) If the number of turns of wire increases then the magnetic strength of electromagnet also increases.
(b) If the number of cells increases i.e. the quantity of electricity increases, the strength of the electromagnet increases.
Question 13.
Name some organisms which can generate electricity in their body. How they use it?
Answer:
There is a system to generate electricity in the bodies of the Jellyfish and electric eel fish. They can generate sufficiently strong electricity. This electricity stuns the enemies and keeps them away.
Long Questions & Answers : (3 marks for each question)
Question 1.
What is LED?
Answer:
The full form of LED is Light Emitting Diode.
It is an electronic device that glows even by a little amount of electricity. It has no filament. Its positive end is larger than the negative end. An LED is not destroyed even in 20 years. Different coloured LEDs are available in the market.
Question 2.
Mention some applications of heating effect of electric current.
Answer:
Some applications of heating effect of electric current are –
a) Electric Iron : Here Nichrome wire is wrapped on Mica. Nichrome wire is heated when electricity is passed through it.
b) Electric Bulb : The filament of bulb made of Tungsten generates heat when electricity is passed through it. Light energy is generated due to transform of heat.
c) Fuse wire : Fuse wire melts at very low temperature. So it is used for the safety of any electrical circuit. When an excess amount of electricity passes through fuse wire due to any reason, it is heated very much and melts. As a result the circuit is cut off and flow of electricity is stopped.
Question 3.
What is solar calculator?
Answer:
Solar calculator is a special type of electronic device. This device runs by electrical energy. Actually solar panel supplies electricity in solar calculator. This panel is constituted by some solar cells. The energy of sunlight is transformed into electrical energy when it falls on solar panel.
Question 4.
Discuss the relation between electrical energy and living world.
Answer:
The relation between electrical energy and living world is very close. The bodies of all living organisms consist of molecules and atoms. Sometimes they can be ionised. At the time of staying in different liquids of living organisms ionised atoms or radicals participate in different physiological activities.
Question 5.
Discuss the influence of electrical energy in the body of human being.
Answer:
a) A special type of component is present in the muscles of heart. The electrical stimulation made by them generates heart beats which is spread in the body in the form of waves.
b) Nerve impulse of brain is also electrical. Brain consists of numerous nerve cells. Different informations are conducted through nerve cells with the help of electrical stimulations. As a result, contraction and expansion of muscles are possible. We can move and do various types of activities.
Question 6.
What is resting potential?
Answer:
In normal situation due to the presence of excess positive charge in the outside of membrance and excess negative charge inside of membrance a potential difference is developed. This is called resting potential. Nerve cells conducts the stimulation only when changes in resting potential occur.