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P位于中点,S2闭合,S1断开:
I=U/(R/2+R2)
R2消耗电功率P2=I^2*R2=U^2*R2/(R/2+R2)^2=6.75W
P从中点移至左端:
I'=U/(R+R2)
I/I'=5/4
得R/R2=2/3,R2=3R/2
代入上式得P2=3(U^2)/8R=6.75W
P2'=I'^2*R2=(4I/5)^2*R2=(16/25)I^2*R2=(16/25)P2=4.32W
S1闭合,S2断开:
I''=U/(R+R1)
R消耗功率:P=I''^2*R=(U^2)*R/(R+R1)^2=8W
由P2=3(U^2)/8R=6.75W,两式相除,得:
R/(R+R1)=2/3
=>R1=R/2
P1=P*R1/R=4W
P1/P2'=4/4.32=0.926
1年前
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