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题:有一个电阻值已看不清楚的电阻R_1,我们想要测出它的电阻值,手边只有一个电池组、一个安培表、一个电阻值看得清楚的电阻器R_2和几根导线。你有办法测R_1的电阻值吗?说出你的办法和理由(见现行初三《物理》183页)。设计一: 1.实验电路如图1。 2.做法: (1)把R_1、R_2换成并联电路后,先把安培表与R_1串联,记下安培表的读数为I_1,于是电池组电压为: U=I_1R_1 ① (2)再把安培表与R_2串联起来,记下安培表读数
Problem: There is a resistor R_1 whose resistance value is not yet clear. We want to measure its resistance value. There is only one battery pack, an ampere meter, a resistor R_2 and several wires at the edge of the resistor. Do you have a way to measure the resistance value of R_1? Say your method and reason (see the current third edition of “Physics” page 183). Design One: 1. The experimental circuit is shown in Figure 1. 2. Practice: (1) After replacing R_1 and R_2 with a parallel circuit, first put the ampere meter in series with R_1 and record the reading of the ampere meter as I_1. Then the battery voltage is: U=I_1R_1 1 (2)Ampere Table in series with R_2 and write down the ammeter reading