Question

A magnet of magnetic moment M is lying along a uniform magnetic field B the work done in rotating the magnet by 90° is

(a) Zero (b)MB/2 (c) MB (d) 2MB

Answer 1

Answer: (C). MB

Explanation: A magnet of magnetic moment M is lying along a uniform magnetic field B the work done in rotating the magnet by $90^{o}$.

We know that,

The work done

$W = \int_{0}^{\theta} \tau\ d\theta$

Given that ,

$\theta = 90^{o}$

So, the work done will be

$W = \int_{0}^{90^{o}} MB\ sin\theta$

$W = MB\ [-cos\theta]_{0}^{90^{o}}$

$W = MB [-cos90^{o} + cos0]$

$W = MB$

Hence, the work done will be MB.

Answer 2

Answer:

Explanation:hn