A superconducting round
ring of radius a and inductance L
was located in a uniform magnetic field of induction B. The ring plane
was parallel to the vector B, and the current in the ring was equal to
zero. Then the ring was turned through 90∘ so that its plane became
perpendicular to the field. Find:
(a) the current induced in the ring after the turn;
(b) the work performed during the turn.