(1)U总=R1×I1=10×0.3=3v (2)R总=U总/I2=3/0.5=6欧姆 R2=1/6-1/10=1/15
并联电路中总电阻等于各电阻的倒数和所以R2=15欧姆 (3)UIt=3×(0.5-0.3)×120=72 j