Question

A circular current loop of magnetic moment M is in an arbitrary orientation in an external magnetic field B. The work done to rotate the loop by 30° about an axis perpendicular to its plane is ______.

Options

• `MB`.

• `sqrt(3) (MB)/2`.

• `(MB)/2`.

• zero.

Answer 1

A circular current loop of magnetic moment M is in an arbitrary orientation in an external magnetic field B. The work done to rotate the loop by 30° about an axis perpendicular to its plane is zero.

Explanation:

As per the diagram, the rotation of the loop by 30° about an axis perpendicular to its plane makes no variation in the angle made by axis of the loop with the direction of magnetic field, i.e.

Therefore, the work done to rotate the loop is given by,

W = MB(cos θ₁ − cos θ₂)

Hence,

W = MB(cos α − cos α) = 0

Work done to rotate the loop is zero.