A short bar magnet of magnetic moment `m=0.32 JT^(-1)` is placed in a uniform magnetic field of 0.15 T. If the bar is free to rotate in the place of the field , which orientation would correspond to its (a) stable , and (b) unstable equilibrium ? What is the potential energy of the magnet in each case ?

Explanation

`m=0.32JT^(-1),b = 0.15T`
a. The bar magnet is directed along the direction of external field so that PE is minimum , `U = - mB = -4.8 xx10^(-2)J` (most stable )
b. Any other position , other than the above is unstable. The one with maximum PE is with the field antiparallel to that of the magnet . In this case.
`U_(max)=mB=4.8xx10^(-2)J`