题目

如图所示，理想变压器的原、副线圈的匝数比为4∶1，原线圈接有u＝311sin 100πt(V)的交变电压，副线圈上接有定值电阻R、线圈L、灯泡D及理想电压表。以下说法正确的是( ) A．副线圈中电流的频率为50 Hz B．灯泡D两端电压为55 V C．若交变电压u的有效值不变，频率增大，则电压表的示数将减小 D．若交变电压u的有效值不变，频率增大，则灯泡D的亮度将变暗听下面一段材料，回答第1-3题。 1. How many people were hurt in the accident? [     ]A. Two. B. Three.C. Four. 2. Where are the speakers going? [     ]A. To a hospital. B. To Carrefour. C. To a concert. 3. How did the woman get to DFC? [     ]A. By bus. B. On foot. C. By taxi.