Physics · Electromagnetic induction and AC · chapter 6 of 14

Class 12 Physics Chapter 6: Electromagnetic Induction Assertion-reason questions with answers

2 assertion-reason questions on Electromagnetic Induction, each with its answer and the reason, written from the NCERT chapter. For the CBSE board, JEE Main and NEET, which are set from the same NCERT chapter. Open a question's solution to check your working; then take the free test to find your next chapter. Each question gives an Assertion (A) and a Reason (R); choose how they stand to each other.

Question 1
Assertion (A): Work has to be done to push the north pole of a bar magnet towards a closed coil. Reason (R): The current induced in the coil makes its face towards the magnet a north pole, which repels the approaching magnet.
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Answer: (a) Both A and R are true, and R is the correct explanation of A.

Both are true. By Lenz's law the induced current opposes the rising flux, so the near face becomes a north pole and repels the magnet; the person pushing does work against this force, and that work appears as Joule heat. R is the reason for A.

Question 2
Assertion (A): The emf induced in a closely wound coil can be increased by increasing its number of turns. Reason (R): Magnetic flux is a scalar quantity measured in weber.
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Answer: (b) Both A and R are true, but R is not the correct explanation of A.

A is true: ε = −N dΦ_B/dt, since the flux change through each turn is the same. R is also true, but the unit and scalar nature of flux do not explain why the emf grows with N.

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