試題詳解

57. A charger for a cell phone contains a transformer that steps down 120-V AC to 5.0-V AC. Suppose the secondary coil contains 30 turns and the charger delivers 700 mA to the phone. Which of the following values is closest to the converted power (W)?
(A)0.2
(B)1
(C)3
(D)10
(E)20