消耗的電能W=轉(zhuǎn)數(shù)n/電能表的參數(shù)N
????=12轉(zhuǎn)/(720轉(zhuǎn)/kW·h)
????=(1/60)kwh
????≈0.017kwh
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設(shè)電流為I
PL=0.4W
UL×I=0.4W
(U-Ur)I=0.4W
(U-IR)I=0.4W
(4-10I)I=0.4
4I-10I2=0.4
10I2-4I 0.4=0
I2-0.4I 0.04=0
(I-0.2)2=0
電路中電流
I=0.2A
電阻R的電壓
Ur=IR=0.2A×10Ω=2V
燈的電阻
RL=U/I-R=4V÷0.2A-10Ω=10Ω
燈的額定功率
P額=U額2/RL=(3.8V)2/10Ω=1.444W