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Concepts Of Physics MCQ Edition [Volume 2]

Exam: Concepts Of Physics MCQ Edition [Volume 2]
Subject: Physics
Chapter: Permanent Magnets

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Permanent Magnets

Let r denote the distance from the centre of a magnetic dipole to a...

Let

r

denote the distance from the centre of a magnetic dipole to a point on its axis. The magnetic field at this point is proportional to

Options

A $\dfrac{1}{r^4}$
B $\dfrac{1}{r^3}$
C $\dfrac{1}{r}$
D $\dfrac{1}{r^2}$

Correct answer

B. $\dfrac{1}{r^3}$

Step-by-step solution

The magnetic field at a distance

r

on the axis of a short magnetic dipole of magnetic moment

M

is given by

B = \dfrac{\mu_0}{4\pi} \dfrac{2M}{r^3}

Therefore, the magnetic field is inversely proportional to the cube of the distance from the centre of the dipole.

B \propto \dfrac{1}{r^3}

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