题干

如图甲所示的电路中,电阻R1的阻值为20Ω,R2为滑动变阻器,其规格能够满足电路要求.电流表A、A1的表盘均如图乙所示,电源电压为12V,且保持不变.闭合开关S,在保持电路元件正常使用的情况下,求:

①电流表A1的示数;

②电路中的最大电功率为多少?此时通过R2的电流I2是多少?

③若R2为一个规格为“30Ω 2A”的滑动变阻器,电流表A的示数变化的最大值△I是多少?

④联系家庭电路,并结合以上计算结果,类比说一说对合理使用家用电器的启示.

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答案(点此获取答案解析)

解:①电流表A1的示数I1=
U
R
1
=

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