NCERT Class 8 Science MCQ | Chapter 4: Electricity: Magnetic and Heating Effects
1. What happens to a magnetic compass placed near a current-carrying wire?
(A) Its needle remains completely stationary
(B) Its needle gets deflected
(C) Its needle stops working permanently
(D) Its needle starts glowing
Answer: (B) Its needle gets deflected
2. What does the deflection of a compass needle near a current-carrying wire indicate?
(A) The wire has become hot
(B) The wire produces a magnetic effect
(C) The wire has become an insulator
(D) The battery has stopped working
Answer: (B) The wire produces a magnetic effect
3. The region around a magnet or a current-carrying wire where its magnetic effect can be felt is called:
(A) Electric field
(B) Magnetic field
(C) Heating zone
(D) Resistance field
Answer: (B) Magnetic field
4. What happens to the magnetic field around a wire when the electric current is stopped?
(A) It becomes stronger
(B) It remains unchanged
(C) It disappears
(D) It changes into heat
Answer: (C) It disappears
5. Who discovered the connection between electricity and magnetism through the deflection of a compass needle?
(A) Alessandro Volta
(B) Hans Christian Oersted
(C) Luigi Galvani
(D) Robert Hooke
Answer: (B) Hans Christian Oersted
6. What is an electromagnet?
(A) A permanent magnet made of steel
(B) A current-carrying coil that behaves like a magnet
(C) A battery containing iron
(D) A magnet that produces electricity without current
Answer: (B) A current-carrying coil that behaves like a magnet
7. Why is an iron core commonly used inside an electromagnet?
(A) It makes the electromagnet stronger
(B) It stops electric current
(C) It prevents the coil from producing heat
(D) It changes electricity into light
Answer: (A) It makes the electromagnet stronger
8. What happens to an electromagnet when the electric current is switched off?
(A) It becomes a stronger permanent magnet
(B) It loses its magnetic effect
(C) It starts producing electricity
(D) Its poles become permanent
Answer: (B) It loses its magnetic effect
9. Which of the following can increase the strength of an electromagnet?
(A) Decreasing the number of turns of the coil
(B) Increasing the number of turns of the coil
(C) Removing the electric current
(D) Using a non-magnetic core only
Answer: (B) Increasing the number of turns of the coil
10. What happens to the strength of an electromagnet when more cells are used with the same coil?
(A) It generally becomes stronger
(B) It becomes weaker
(C) It loses all magnetic effect
(D) It becomes a permanent magnet
Answer: (A) It generally becomes stronger
11. How can the poles of an electromagnet be reversed?
(A) By changing the direction of electric current
(B) By increasing the length of the wire only
(C) By removing the iron core
(D) By reducing the number of paper clips
Answer: (A) By changing the direction of electric current
12. What is a lifting electromagnet mainly used for?
(A) Lifting and sorting heavy iron or steel objects
(B) Measuring temperature
(C) Producing drinking water
(D) Increasing the brightness of sunlight
Answer: (A) Lifting and sorting heavy iron or steel objects
13. Why can a lifting electromagnet easily release the objects it has lifted?
(A) The iron objects become non-magnetic permanently
(B) Switching off the current removes the magnetic effect
(C) The electromagnet becomes hotter
(D) The objects lose their mass
Answer: (B) Switching off the current removes the magnetic effect
14. What happens when electric current flows through a conductor?
(A) The conductor always becomes an insulator
(B) The conductor produces a magnetic field and gets heated
(C) The conductor stops producing any effect
(D) The conductor becomes permanently magnetic
Answer: (B) The conductor produces a magnetic field and gets heated
15. Why does a nichrome wire become warm when electric current passes through it?
(A) It absorbs heat from the surroundings
(B) Its resistance converts some electrical energy into heat energy
(C) It produces heat through photosynthesis
(D) It receives heat from the battery only
Answer: (B) Its resistance converts some electrical energy into heat energy
16. What is the heating effect of electric current?
(A) Production of light by a cell
(B) Generation of heat in a conductor due to electric current
(C) Production of magnetism by a battery
(D) Cooling of a conductor by electricity
Answer: (B) Generation of heat in a conductor due to electric current
17. Which of the following appliances works mainly on the heating effect of electric current?
(A) Electric iron
(B) Compass
(C) Electromagnet crane
(D) Loudspeaker
Answer: (A) Electric iron
18. What is the function of a heating element in an electrical appliance?
(A) It produces heat when electric current passes through it
(B) It prevents all current from flowing
(C) It produces a magnetic field only
(D) It stores electrical energy permanently
Answer: (A) It produces heat when electric current passes through it
19. Which material is commonly used for making heating elements?
(A) Nichrome
(B) Pure water
(C) Wood
(D) Glass
Answer: (A) Nichrome
20. Which factor affects the amount of heat generated in a wire?
(A) Material of the wire
(B) Thickness of the wire
(C) Length of the wire
(D) All of the above
Answer: (D) All of the above
21. Why is it important to use wires, plugs, and sockets rated for the specified current?
(A) To prevent unnecessary heating and possible damage
(B) To increase the weight of the appliance
(C) To stop all electrical current
(D) To make the appliance work without electricity
Answer: (A) To prevent unnecessary heating and possible damage
22. What produces electricity in a Voltaic cell?
(A) A magnetic field
(B) A chemical reaction between the electrodes and electrolyte
(C) Heating of the electrodes
(D) Movement of air
Answer: (B) A chemical reaction between the electrodes and electrolyte
23. What is the electrolyte in a Voltaic cell?
(A) A solid metal rod only
(B) A liquid, usually a weak acid or salt solution
(C) A plastic container
(D) A connecting wire
Answer: (B) A liquid, usually a weak acid or salt solution
24. Which statement correctly describes a dry cell?
(A) Its electrolyte is a thick moist paste
(B) Its electrolyte is always pure water
(C) It can be recharged unlimited times
(D) It contains no electrodes
Answer: (A) Its electrolyte is a thick moist paste
25. Which statement about rechargeable batteries is correct?
(A) They can be recharged and reused multiple times
(B) They can never be recharged
(C) They work only in electric heaters
(D) They contain no chemical substances
Answer: (A) They can be recharged and reused multiple times
NCERT Class 8 Science MCQ | Chapter 4: Electricity: Magnetic and Heating Effects
Assertion–Reason Questions
Directions:
Choose the correct option:
(A) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
(B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
(C) Assertion is true, but Reason is false.
(D) Assertion is false, but Reason is true.
1. Assertion: A compass needle gets deflected when placed near a current-carrying wire.
Reason: Electric current flowing through a conductor produces a magnetic field around it.
Answer: (A)
2. Assertion: An electromagnet loses its magnetic effect when the electric current is switched off.
Reason: The magnetic field produced by the current-carrying coil disappears when the current stops flowing.
Answer: (A)
3. Assertion: An iron core makes an electromagnet stronger.
Reason: When an iron nail is inserted inside a current-carrying coil, the magnetic effect of the coil becomes stronger.
Answer: (A)
4. Assertion: Nichrome wire is used in many electrical heating appliances.
Reason: Nichrome has higher resistance than a copper wire of the same size and length, causing more electrical energy to be converted into heat.
Answer: (A)
5. Assertion: Rechargeable batteries can be used multiple times.
Reason: Rechargeable batteries can be recharged after their stored electrical energy has been used.
Answer: (A)
