Question

The magnetic moment of a magnet is $0.1 \,amp \times m ^2$. It is suspended in a magnetic field of intensity $3 \times 10^{-4}$ weber/ $m ^2$. The couple acting upon it when deflected by $30^{\circ}$ from the magnetic field is

• A. $1 \times 10^{-5}\, N m$
• B. $1.5 \times 10^{-5} \,Nm$
• C. $2 \times 10^{25}\, Nm$
• D. $2.5 \times 10^{-5}\, N m$

Answer 1

Answer: (B)

$\tau= MB \sin \theta=0.1 \times 3 \times 10^{-4} \sin 30^{\circ}$
or $\tau=1.5 \times 10^{-5} N - m$