Question

为了使得标有“110V 100W”和“110V 40W”的L1、L2两灯接入220V电路中能正常发光,并且能电路消耗的功

Answer 1

L1：P1= U*U/R1 R1 = U*U/P1 = 110*110/100 = 121 Ω

L2：P2= U*U/R2 R2 = U*U/P2 = 110*110/40 = 302.5 Ω

要使两灯都能正常发光,就必须使两灯上电压都正好是110V,也就是说必须使灯L2与变阻器并联后的电阻与灯L1的电阻相等,为121 Ω

1/R = 1/R2 +1/R3 1/121 = 1/302.5 +1/R3 R3 = 201.67 Ω

电路中所消耗的功率应为两灯额定功率加上电阻所消耗的功率,即P= P1+P2+P3 = 100+40+P3,所以P3越小,电路中所消耗的总功率就越小.