question_answer 33)

  A circular current loop of magnetic moment M is in an arbitrary orientation in an external magnetic field . The work done to rotate the loop by about an axis perpendicular to its plane is (a) MB                                  (b) (c)                                 (d) zero

Answer:

  (d)Let magnetic moment  of current loop be making an angle  with the direction of . When a current circular loop is rotated in a magnetic field by 30° about an axis perpendicular to its plane, there is no change in the angle between magnetic moment  and magnetic field . Therefore, = , = . Workdone,