Question

A closely wound solenoid of $2000$ turns and area of cross-section $1.5 \times 10^{-4} m ^{2}$ carries a current of $2.0 A$. It is suspended through its center and perpendicular to its length, allowing it to turn in a horizontal plane in a uniform magnetic field $5 \times 10^{-2} T$, making an angle of $30^{\circ}$ with the axis of the solenoid. The torque on the solenoid will be

• A. $3 \times 10^{-3} N - m$
• B. $1.5 \times 10^{-3} N - m$
• C. $1.5 \times 10^{-2} N - m$
• D. $3 \times 10^{-2} N - m$

Answer 1

The Correct Option is C

$\tau =N i B A \sin \theta$ $=2000 \times 2 \times 5 \times 10^{-2} \times 1.5 \times 10^{-4} \times \sin 30^{\circ}$ $=2000 \times 50 \times 10^{-6} \times \frac{1}{2}$ $=1.5 \times 10^{-2} N - m$