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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

Suppose r represents the distance of a point on the axis of a bar...

Suppose

r

represents the distance of a point on the axis of a bar magnet from its centre. The magnetic field at this location is proportional to

Options

A $\dfrac{1}{r^3}$
B $\dfrac{r}{(r^2 - l^2)^2}$ (where $2l$ is the magnet's length)
C $\dfrac{1}{r}$
D $\dfrac{1}{r^2}$

Correct answer

B. $\dfrac{r}{(r^2 - l^2)^2}$ (where $2l$ is the magnet's length)

Step-by-step solution

The magnetic field due to a bar magnet of length

2l

and magnetic dipole moment

M

at a point on its axial line at a distance

r

from the centre is given by

B = \dfrac{\mu_0}{4\pi} \dfrac{2Mr}{(r^2 - l^2)^2}

Therefore, the magnetic field is proportional to

\dfrac{r}{(r^2 - l^2)^2}

.

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