Question

A circular current loop of magnetic moment M is in an arbitrary orientation in an external magnetic field $\overline{B}$. The work done to rotate the loop by 30 about an axis perpendicular to its plane is:

• A. $MB$
• B. $\sqrt{3}\frac{MB}{2}$
• C. $\frac{MB}{2}$
• D. $zero$

Answer 1

Answer: (D)

$zero$

The rotation of the loop by $30°$ about an axis perpendicular to its plane make no change in the angle made by axis of the loop with the direction of magnetic field, therefore, the work done to rotate the loop is zero.

Important point: The work done to rotate the loop the loop in magnetic field $W=MB(cos{\theta }_1-cos{\theta }_2)$, where signs are as usual.