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Important Questions Chapter 4 Class 8 Science Curiosity CBSE Board

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Electricity: Magnetic and Heating Effects


Short Questions

1. What happens to a compass needle when current flows through a wire nearby?
Answer: It deflects from its original direction.

2.What is the magnetic effect of electric current?
Answer: Electric current in a wire creates a magnetic field around it.

3.What is an electromagnet?
Answer: A coil with current that acts like a magnet.

4.How can you make an electromagnet stronger?
Answer: Increase the current or number of coil turns.

5.What happens to an electromagnet when the current stops?
Answer: It loses its magnetic effect.

6.What is the heating effect of electric current?
Answer: Current passing through a conductor produces heat.

7.Why does a nichrome wire heat up more than a copper wire?
Answer: Nichrome has higher resistance than copper.

8.What is a Voltaic cell?
Answer: A cell that generates electricity from chemical reactions.

9.What is the electrolyte in a lemon cell?
Answer: Lemon juice.

10.What is a dry cell?
Answer: A cell with a paste-like electrolyte, not liquid.

11.Can all batteries be recharged?
Answer: No, only rechargeable batteries can be recharged.

12.What are the poles of an electromagnet like?
Answer: It has North and South poles, like a bar magnet.

13.What is used in electric heaters to produce heat?
Answer: A heating element, like a nichrome coil.

14.Why do rechargeable batteries wear out?
Answer: They lose capacity after many charge cycles.

15.Why should batteries be recycled?
Answer: To avoid environmental harm and reuse valuable materials.


Long Questions

1. How can you test if current is flowing in a circuit without an electric lamp?
Answer: Use a magnetic compass near the wire; if the needle deflects, current is flowing. This happens because current produces a magnetic field.

2.How can you make a temporary magnet using electricity?
Answer: Wrap a wire around an iron nail and pass current through it. This creates an electromagnet that acts as a magnet only when current flows.

3.Why does a compass needle deflect near a current-carrying wire?
Answer: The current creates a magnetic field around the wire. This field affects the compass needle, causing it to move.

4.What happens to an electromagnet’s strength if you add more cells?
Answer: More cells increase the current, making the magnetic field stronger. This causes greater deflection of a compass needle or attracts more clips.

5.Why does a nichrome wire heat up when current flows through it?
Answer: Nichrome has high resistance, which converts electrical energy into heat. More current or longer flow increases the heat produced.

6.How does a Voltaic cell generate electricity?
Answer: Chemical reactions between two metal electrodes and an electrolyte produce electricity. The current flows from the positive to the negative terminal.

7.Why do some household appliances get warm when used?
Answer: Electric current passes through their heating elements, causing resistance. This resistance converts electrical energy into heat.

8.What are the advantages of electric heating devices over burning wood?
Answer: Electric heaters are cleaner, easier to control, and don’t produce smoke. They are also more efficient and safer for indoor use.

9.What happens if you reverse the battery terminals in an electromagnet circuit?
Answer: The direction of the current reverses, switching the electromagnet’s poles. This changes the direction of the compass needle deflection.

10.Why is it important to dispose of batteries properly?
Answer: Batteries contain harmful chemicals like acids and metals that can damage the environment. Recycling them recovers valuable materials and prevents pollution.

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