Problem 3.323

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 \(\mathbf{B}\), and the current in the ring was equal to zero. Then the ring was turned through \(90^{\circ}\) 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.