Question

Magnetism at the centre of a bar magnet is:

• A. Minimum
• B. Maximum
• C. Zero
• D. Minimum or maximum

Hint:

Think about where the pull of the north pole and the pull of the south pole exactly balance out.

Answer 1

The Correct Option is C

Model the bar magnet as two point poles, a north pole of strength $+m$ near one end and a south pole of strength $-m$ near the other end, with the two poles separated by a length $2l$.

1. At any point on the axis of the magnet, the magnetic field from the north pole and the magnetic field from the south pole act in opposite senses along that axis.
2. At the exact centre of the magnet, the distance to the north pole equals the distance to the south pole, so the two fields have exactly equal magnitude.
3. Because the magnitudes are equal and the directions are opposite, the resultant magnetic field at this single point works out to be zero.
4. This is why the centre of a bar magnet is often called its neutral point, the one place inside the magnet where the pole effects balance out fully.

So option C, zero, is correct.