Q.

A circular coil having 200 turns, 2.5×10-4m2 area and carrying 100 μA current is placed in a uniform magnetic field of 1 T. Initially, the magnetic dipole moment (M) was directed along  B. Amount of work, required to rotate the coil through 90° from its initial orientation such that M becomes perpendicular to B, is ____ μJ.           [2024]


Ans.

(5)

Work done by external magnetic field ΔU=Uf-Ui

Initially, Ui=-MBcosθ=-MBcos0°=-MB

Finally, Uf=-MBcos90°=0

The magnetic moment of coil, M=NiA

M=(100×10-6)·(200)·(2.5×10-4)

Work, W=ΔU=MB=(5×10-6)(1)=5μJ