Lag1989 problem number 16.50

A circular contour of radius R = 20mm is placed in a uniform magnetic field whose induction is B = 50 mT, so that the contour plane is perpendicular to the field lines of force. A constant current I = 2 A is maintained in the circuit. What work needs to be done to turn the circuit 90 ° around an axis that coincides with the diameter of the circuit?