A short bar magnet of magnetic moment `m= 0.32 J T^(-1)` is placed in a unifrom magnetic field of 0.15T. If the bar is free to rotate in the plane of
A short bar magnet of magnetic moment `m= 0.32 J T^(-1)` is placed in a unifrom magnetic field of 0.15T. If the bar is free to rotate in the plane of the field, which orientation would corresponds to its (a) stable, and (b) unstable equilibrium ? What is the potential energy of the magnet in each case ?
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Here `m = 0.32 J T^(-1), B = 0.15 T`
(i) In stable equilibrium, the bar magnet is aligned along the magnetic field i.e., `theta = 0^(@)`.
Potential Energy `= -mB cos 0^(@) = -0.32 xx 0.15 xx 0 = -4.8 xx 10^(-2)J`.
(ii) In unstable equilibrium the magnet is so oriented that magnetic moment is at `180^(@)` to the magnetic field i.e., `theta = 180^(@)`.
Potential Energy `= mB cos 180^(@) = -0.32 xx 0.15^(-1) = 4.8 xx 10^(-2)J`.
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