s1闭合,s2断开,U=R1*0.2 .(1)
S1,s2都闭合,U=10*R1/(10+R1) *0.5;.(2)
联立(1)(2)得R1=15Ω U=3V
P1=U^2/R1=3^2//15=0.6W
P2=U^2/R2=3^2//10=0.9W
W2=P2*t=0.9*60=54 J
s1闭合,s2断开,U=R1*0.2 .(1)
S1,s2都闭合,U=10*R1/(10+R1) *0.5;.(2)
联立(1)(2)得R1=15Ω U=3V
P1=U^2/R1=3^2//15=0.6W
P2=U^2/R2=3^2//10=0.9W
W2=P2*t=0.9*60=54 J