如图电路,R2=20欧,电源电压保持不变,当S1,S2都闭合时电流表的示数为0.6安,当S1闭合,S2断开时电流表的示数

S1、S2都闭合时只有R1接入电路中
电源电压 U = I1 R1 = 0.6R
S2 断开时R1、R2均接入回路
电源电压 U = I2 (R1+R2) = 0.2R1+0.2*20

0.6R1 = 0.2R1+4
R1 = 10Ω
电源电压 U = 0.6R1 = 0.6*10 = 6V