Question

A short bar magnet of magnetic moment $0.4J{T}^{-1}$ is placed in a uniform magnetic field of 0.16 $T$. The magnet is in stable equilibrium, when the potential energy is

• A. 0.064 $J$
• B. -0.064 $J$
• C. zero
• D. 0.082 $J$

Answer 1

The correct option is B -0.064 $J$

Here, Magnetic moment, $M$=$0.4J{T}^{-1}$
, $B$=0.16 $T$
When a bar magnet of magnetic moment $M$ is placed in a uniform magnetic field, it's potantial energy is$U=-M.B=-MB\cos \left(\theta \right)Forstableequlibrium,\theta =0^0\therefore U=-MB=-(0.4J{T}^{-1})(0.16T)=-0.064J$