如图 所示,电源供电电压 U = 220 V ,每根输电导线的电阻均为 R 1 = 1 W ,电路中一共并联 100 盏额定电压 220V 、功率 40 W 的电灯。假设电灯正常发光时电阻值为常数。试求: ( 1 ) 当只有 10 盏电灯工作时,每盏电灯的电压 U L 和功率 P L ; ( 2 ) 当 100 盏电灯全部工作时,每盏电灯的电压 U L 和功率 P L
【单选题】Presently available power semiconductor devices can be classified into three groups according to their degree of controllability. Which one is not in the three groups? ( )