4.9 A square coil of side 10 cm consists of 20 turns and carries a current of 12 A. The coil is suspended vertically and the normal to the plane of the coil makes an angle of 30º with the direction of a uniform horizontal magnetic field of magnitude 0.80 T. What is the magnitude of torque experienced by the coil?

NEETprep Answer:
Length of a side of the square coil, l = 10 cm = 0.1 m
Current flowing in the coil, I = 12 A
Number of turns on the coil, n = 20
Angle made by the plane of the coil with magnetic field, θ=30°
Strength of magnetic field, B = 0.8 T
Magnitude of the magnetic torque experienced by the coil in the magnetic field is given by the relation,
τ=n BIAsinθ
Where, A = Area of the square coil
=1×1=0.1×0.1
=0.01 m2
So,
τ=20×0.8×12×0.01×sin30°
=0.96 N m
Hence, the magnitude of the torque experienced by the coil is 0.96 N m.