Question

The torque and magnetic potential energy of a magnetic dipole in most stable position in a uniform magnetic field $\left(\overline{B}\right)$ having magnetic moment $\left(\overline{m}\right)$ will be

• A. $-mB,zero$
• B. $mB,zero$
• C. $zero,mB$
• D. $zero,-mB$

Answer 1

The correct option is D $zero,-mB$

Torque, $\overline{T}=\overline{m}\times \overline{B}=mBsin\theta$
and magnetic potential energy $U_m=\overline{m}.\overline{B}=mBcos\theta$ at $\theta =0^0$ the dipole will be in most stable position
$T=mBsin\theta =mBsin{0}^0=0$
and $U_m=-mBcos\theta =-mBcos{0}^0=-mB$