(1)电阻R1的阻值,(2)滑动变阻器R3的最大电阻,(3)电源电压U.

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  • 设电源电压为U

    U/(R1+R2+R3)XR1=3

    U=0.45×(R1+R2+1/2R3)

    U/(R1+R2)XR1=9