The torque and magnetic potential energy of a magnetic dipole in most stable position in a uniform magnetic field `vec(B)` having magnetic moment `vec(m)` will be

Options

A. `-mB,zero`
B. `mB,zero`
C. `zero,mB`
D. `zero,-mB`

Answer

D

Explanation

Torque, `"Torque", vec(tau)=vec(m)xxvec(B)=mB sin theta`
and magnetic potential energy `U_(m)=vec(m).vec(B)=mB sin theta`
`theta=0^(@)` the dipole will be in most stable position
`pi=mB sin theta=mB sin 0^(@)=0`
`and U_(m)=-mB cos theta=-mBcos 0^(@)=-mB`