International Development homework help. A toroid having a rectangular cross section (a = 2.00 cm by b = 3.00 cm) and inner radius R = 3.90 cm consists of 500 turns of wire that carries a sinusoidal current I = Imax sin ?t, with Imax = 48.0 A and a frequency f = ?/2? = 60.0 Hz. A coil that consists of 20 turns of wire links with the toroid, as shown in Figure P31.17. Determine the emf induced in the coil as a function of time. V) cos?t