Question

A circular coil of 25 turns and radius 12 cm is placed in a uniform magnetic field of 0.5 T normal to the plane of the coil. If the current in the coil is 6 A then total torque acting on the coil is

• A. Zero
• B. 3.4 N m
• C. 3.8 N m
• D. 4.4 N m

Answer 1

Answer: (A)

Zero

Answer 2

The torque acting on the coil

$| \vec { \tau } | = | \overrightarrow { \mathrm { m } } \times \overrightarrow { \mathrm { B } } | = \mathrm { mB } \sin \theta$ here the circular coil is placed normal to the direction of magnetic field then the angle between the direction of magnetic moment and magnetic field $( \vec { B } )$ is zero, then

$\tau = \mathrm { mB } \sin \theta = \mathrm { mB } \sin 0 = 0 \quad \therefore \tau = 0$