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)

150 $\hat { k } N - m$

Answer 2

$\vec { \tau } = \vec { M } \times \vec { B } \Rightarrow \vec { \tau } = 50 \hat { i } \times ( 0.5 \hat { i } + 3 \hat { j } )$

$= 150 ( \hat { i } \times \hat { j } ) = 150 \hat { k } N \times m$