Physics · Magnetism · chapter 5 of 14

Class 12 Physics Chapter 5: Magnetism and Matter Assertion-reason questions with answers

2 assertion-reason questions on Magnetism and Matter, 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): The net magnetic flux through any closed surface is zero. Reason (R): Isolated magnetic poles do not exist, so magnetic field lines form closed loops and every line entering a closed surface also leaves it.
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Answer: (a) Both A and R are true, and R is the correct explanation of A.

Both are true. Because there are no sources or sinks of B (no monopoles), lines entering a closed surface balance those leaving it; this is exactly why the net flux is zero.

Question 2
Assertion (A): A bar magnet suspended freely comes to rest roughly along the geographic north–south direction. Reason (R): Two magnetic field lines never intersect.
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Answer: (b) Both A and R are true, but R is not the correct explanation of A.

Both are true. A suspended magnet points north–south because the earth behaves as a magnet. That field lines do not cross (the direction of B must be unique at every point) is a separate fact and does not explain the orientation.

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