Question

A coil 2.0 cm in diameter has 300 turns. If the coil carries a current of 10 mA and lies in a magnetic field $5\times {10}^{-2}$ T, the maximum torque experienced by the coil is:

• A. $4.7\times {10}^{-2}$ N-m
• B. $4.7\times {10}^{-4}$ N-m
• C. $4.7\times {10}^{-5}$ N-m
• D. $4.7\times {10}^{-8}$ N-m

Answer 1

The correct option is A $4.7\times {10}^{-2}$ N-m

Magnetic moment of experienced carrying loop $\to M=niA$

$M=niA\to ni\left(\pi r^2\right)$

work done

$\downarrow$

$w=MB(1-\cos \theta )=2MB$

$=2\left(ni\pi r^2\right)B$

$2\times 300\times 0.01A\times 3.14\times 0.1\times 0.1\times 5\times {10}^{-2}$

$\zeta =0.0047\Rightarrow 4.7\times {10}^{-2}N.M$