Question

The work done in rotating a magnet of magnetic moment $2A-m^2$ in a magnetic field of $5\times {10}^{-3}T$ from the direction along the magnetic field to opposite direction to the magnetic field, is

• A. Zero
• B. $2\times {10}^{-2}J$
• C. ${10}^{-2}J$
• D. $10J$

Answer 1

The correct option is B $2\times {10}^{-2}J$

$W=MB(1-cos\theta )$; where $\theta ={180}^{\circ }$
$\Rightarrow W=2MB\Rightarrow W=2\times 2\times 5\times {10}^{-3}=2\times {10}^{-2}J$