Question

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

• A. $4.7\times {10}^{-5}$N-m
• B. $5\times {10}^{-4}$N-m
• C. $5\times {10}^{-5}$N-m
• D. $5\times {10}^{-6}$N-m`

Answer 1

The correct option is A $4.7\times {10}^{-5}$N-m

$area=\frac{\pi d^2}{4}=\frac{\pi }{4}\times 2\times {10}^{-4}=\pi \times {10}^{-4}M=300I=10\times {10}^{-3}AB=5\times {10}^{-2}T\tau =MBIA=300\times 5\times {10}^{-2}\times 10\times {10}^{-3}\times \pi \times {10}^{-4}=4.7\times {10}^{-5}$ N-m