题干

如图所示的电路中,电源电压保持不变,R1=3Ω.当S断开时,电流表的示数为2A,当S闭合后,电流表的示数为3A,求电源电压和R2的阻值.

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答案(点此获取答案解析)

解:①当S断开时,电路为R1的简单电路,电流表测R1支路的电流,
由I=
U
R
可得,电源的电压:
U=I1R1=2A×3Ω=6V;
②当S闭合

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