W1=U²t/R1=160
W2=U²t/R2=40
所以R1/R2=160/40=4/1
又
W1=UI2t
W总=UIt
由于总电阻(R1+R2)是R2的5倍,所以I是I2的1/5.
所以W总是W2的1/5,
W总=40/5=8J