The Total solution for NCERT class 6-12
A short bar magnet ofmagnetic moment m = 0.32 J T−1 is placed in a uniformmagnetic field of 0.15 T. If the bar is free to rotate in the plane of thefield, which orientation would correspond to its (a) stable, and (b) unstableequilibrium? What is the potential energy of the magnet in each case?
Moment of the barmagnet, M = 0.32 J T−1
External magneticfield, B = 0.15 T
(a)The bar magnet isaligned along the magnetic field. This system is considered as being in stableequilibrium. Hence, the angle θ, between the bar magnet and themagnetic field is 0°.
(b)The bar magnet isoriented 180° to the magnetic field. Hence, it is in unstable equilibrium.
θ = 180°
Potential energy =− MB cos θ