| 如图所示，处在磁感应强度为B的匀强磁场中的单匝矩线圈abcd，以恒定的角速度ω绕ab边转动，磁场方向垂直于纸面向里，线圈所围面积为S，线圈导线的总电阻为R．t=0时刻线圈平面与纸面重合，且cd边正在离开纸面向外运动．则正确的是（ ） A．时刻t线圈中电流的瞬时值i B．线圈中电流的有效值I C．线圈中电流的有效值I= D．线圈消耗的电功率P  |
答案：C
| 阅读下面短文，将短文后的五个选项中选出能填入空白处的最佳选项。选项中有一项为多余选项。 | |
| Mr. Johnson worked in a restaurant. He worked there for ten years. 1 . And at last he was sent away. He hated hard work and stayed in the city. Once something was wrong with his ear. He had to see a doctor. 2 . And five minutes later he had to pay the doctor twenty dollars. He thought it was easy to get much money. So he came to the small town and opened a hospital. At first the people there knew nothing about him and they came to see him. But soon they found he couldn't treat them at all and his medicine wasn't useful. People hardly came and he had nothing to do. One evening he heard a knock at the door. 3 . He thought he had a bad cold and he asked him to take some medicine. After that the man left. 4 . On the third day a young man came in and said, "Thank you very much, doctor ! "It surprised Mr. Johnson. He said, "I haven't seen you before. What do you thank me for?" My uncle died from your wrong treatment the day before yesterday and he left much money to me.
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cosωt
