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AIIMS2018Physics-Magnetism

AIIMS 2018 Physics Magnetic Field MCQ Question

Type: MCQ-conceptual-Medium-Class 12

A bar magnet has length 8 cm8\text{ cm}. The magnetic field at a point at a distance 3 cm3\text{ cm} from the centre in the broad side-on position is found to be 4×10−6 T4 \times 10^{-6}\text{ T}. The pole strength of the magnet is:

A

6×10−5 Am6 \times 10^{-5}\text{ Am}

B

5×10−5 Am5 \times 10^{-5}\text{ Am}

C

2×10−4 Am2 \times 10^{-4}\text{ Am}

D

3×10−4 Am3 \times 10^{-4}\text{ Am}

Correct Answer

Option A

Detailed Explanation

In the given formula for the magnetic field BB due to a bar magnet in the broad-side on position, B=μ04πM[r2+l24]B = \frac{\mu_0}{4\pi} \frac{M}{\left[r^2 + \frac{l^2}{4}\right]}, the term M=mlM = ml represents the magnetic moment, where mm is the pole strength and ll is the length of the magnet. This equation accurately describes the magnetic field's dependence on the distance rr from the magnet and its physical dimensions, confirming that option A is correct. Since all other options are marked as N/A, they do not provide any alternative explanations or values relevant to the question, making them irrelevant in this context.

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