Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): The net magnetic flux through a closed surface that encloses only the north pole of a bar magnet is zero.
Reason (R): The magnetic field of a bar magnet is strongest near its two ends (poles).
In the light of the above statements, choose the most appropriate answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → Both (A) and (R) are correct but (R) is NOT the correct explanation of (A).
Assertion (A) The net magnetic flux through a closed surface that encloses only the north pole of a bar magnet is zero. — True. Gauss’s law for magnetism holds for every closed surface, also for one drawn around a single pole.
Reason (R) The magnetic field of a bar magnet is strongest near its two ends (poles). — True. The field is strongest at the ends and weakest in the central region of the magnet.
Why Reason (R) does not explain Assertion (A)?
R tells only how strong the field is near a pole. The strength of the field does not decide whether the net flux is zero.
The flux is zero because magnetic field lines form closed loops. Inside the magnet the lines run from the S-pole to the N-pole. So the lines that leave the surface outside the magnet enter it again inside the magnet.
NCERT (2026-27):
Example 5.3 – “(e) Right. These are field lines outside and inside a bar magnet. Note carefully the direction of field lines inside. Not all field lines emanate out of a north pole (or converge into a south pole). Around both the N-pole, and the S-pole, the net flux of the field is zero.”
Example 5.1 – “… In a bar magnet the intensity of the magnetic field is the strongest at the two ends (poles) and weakest at the central region. …”