A current carrying loop is free to turn in a uniform magnetic field.The loop will then come into equilibrium when its plane is inclined at

Options

A. `0^(@)` to the direction of the field
B. `45^(@)` to the directed of the field
C. `90^(@)` to the directed of the field
D. `135^(@)` to the directed of the field

Answer

C

Explanation

`U =-vec(M) . vec(B) = -MB cos theta`
Equilibrium will be stable if `U` is minimum. It will happen when
`theta =0^(@), U_(min) = -MB`