1.两个相同的白炽灯泡L1和L2接到图1的电路中,灯L1与电容器串联,灯L2与电感线圈串联.当a、b间接电压最大值为Um、频率为f的正弦交流电源时,两灯都发光,且亮度相同.更换一个新的正弦交流电源后,灯L1的亮度低于灯L2的亮度.新电源两极的电压最大值和频率可能是() 1. Two identical incandescent bulbs, L1 and L2, are connected to the circuit of Figure 1. The lamp L1 is connected in series with the capacitor and the lamp L2 is in series with the inductor winding. When the maximum indirect voltage across a and b is Um, a sinusoidal alternating current source of frequency f , Both lights glow and have the same brightness. After replacing a new sinusoidal AC power source, lamp L1 has a lower brightness than lamp L2 The maximum voltage and frequency at the new power supply poles may be ()