右 图中的 RL 串联支路为直流电动机励磁绕组的等效电路, R 1 支路是励磁回路的泄放电路。电源电压 U S =200V , R =10 W , L =1.25H ,在 t =0 时开关断开。试求: ( 1 )在断开瞬间绕组上的电压不超过 250V ,需要并联多大的泄放电阻 R 1 ? ( 2 )开关断开后,经过多长时间使电流衰减到初始值的 5% ?
【简答题】A.It is too late for the man to buy a ticket for the concert. B.The man must wait for two hours to buy a ticket. C.People have already been standing in line for two hours. D.The man can buy a standing...