試題詳解

46. As shown in the figure, a wire and a 10-Ω resistor are used to form a circuit in the shape of a square, 20 cm by 20 cm. A uniform but nonsteady magnetic field is directed into the plane of the circuit. The magnitude of the magnetic field is decreased from 1.50 T to 0.50 T in a time interval of 63 ms. The average induced current and its direction through the resistor, in this time interval, are closest to

(A) 63 mA, from b to a
(B) 38 mA, from b to a
(C) 63 mA, from a to b
(D) 38 mA, from a to b
(E) 95 mA, from a to b.