Question

A magnet of magnetic moment $50 \hat{ i } A - m ^{2}$ is placed along the $x$ -axis in a magnetic field $\vec{B}=(0.5 \hat{i}+3.0 \hat{j}) T$. The torque acting on the magnet is:

• A. $175 \hat{ k } N - m$
• B. $150 \hat{ k } N - m$
• C. $75 \hat{ k } N - m$
• D. $25 \sqrt{37} \hat{ k } N - m$

Answer 1

Answer: (B)

$\vec{\tau}=\vec{ M } \times \vec{ B }$
$=50 \hat{ i } \times(0.5 \hat{ i }+3 \hat{ j })$
$=150(\hat{ i } \times \hat{ j })=150 \hat{ k } N - m$