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例1 在如图1所示电路里,电源电压保持不变,滑动变阻器的最大阻值为R,并且R>R1.变阻器滑片P从a向b滑动的过程中,滑动变阻器消耗的电功率将( ). (A)逐渐变大(B)逐渐变小(C)先变大后变小(D)先变小后变大分析:①当P从a向b滑动时,变阻器接入电路电阻变大.滑动变阻器两端电压逐渐增大,但通过它的电流却逐渐减小,滑动变阻器消耗的电功率的变化无法直接由P=UI确定.
Example 1 In the circuit shown in Figure 1, the power supply voltage remains constant, the maximum resistance of the sliding rheostat is R, and R>R1. The varistor slide P slides from a to b, the electrical power consumed by the sliding rheostat will be (). (A) gradually becomes larger (B) gradually becomes smaller (C) becomes larger first and then becomes smaller (D) becomes smaller first and then becomes larger Analyze: 1 When P moves from a to b, the varistor is connected to the circuit resistance Larger. The voltage across the sliding rheostat gradually increases, but the current through it gradually decreases, and the change in the electrical power consumed by the sliding rheostat cannot be directly determined by P=UI.