Question

What done in rotating a bar magnet of magnetic moment?

Answer 1

Answer:

Explanation:

when a bar magnet is in unstable equilibrium then its angle with the magnetic field will be 180 degree while when bar magnet is in stable equilibrium then its angle with magnetic field will be 0 degree

Now in order to find the work done we can say

W = U_f - U_i

here U = potential energy of bar magnet

so we will have

U = - M.B

U = - MBcos\theta

now by plug in the value

U = -MBcos\theta_f + MBcos\theta_i

also we know that

\theta_f = 0 degree

\theta_i = 180 degree

now we have

W = -MBcos0 + MBcos180

W = -2MB

so work done to change the orientation of magnet is - 2MB