学生在做《用惠斯通电桥测电阻》的实验时,经常会出现一些故障现象。其中常见的是,在滑动触头移动过程中,电流计中有电流但找不到平衡位置,或者平衡位置在极端位置(图一中的A或C)。现就以下两种情况作一简要的分析讨论。第一种情况故障现象如图一所示,滑动触头D由A向C移动,电流计G中的电流逐渐增大,当D处左边极端位置A时,电流计指针才不发生偏转。故障原因BC段线路断路(即Rx断路或线路假接)。分析讨论 1.当不计电源内阻r和变阻器R′时,外电路电阻为 When students are doing experiments with Wheatstone bridge resistance, there are often some malfunctions. It is common that during the movement of the sliding contact, there is current in the ammeter but no equilibrium position is found, or the equilibrium position is in the extreme position (A or C in Figure 1). A brief analysis and discussion will be made on the following two situations. In the first case, the fault phenomenon is shown in Fig. 1. The sliding contact D moves from A to C. The current in the current meter G gradually increases. When the left extreme position A at D, the current meter pointer does not deflect. Cause of fault BC segment line is open (ie Rx disconnected or line dummy). Analysis and Discussion 1. When the internal resistance r and varistor R′ are not taken into account, the external circuit resistance is