问题 选择题

图中电路的电源电压不变,当变阻器的滑片P向右移动时,正确的结论是(  )

A.A,B,C三灯全部变暗

B.A,B两灯亮度不变,C灯变暗

C.A,C两灯变暗,B灯变亮

D.A,B两灯变亮,C灯变暗

答案

当滑片P向右移动时,连入电路中的电阻增大,并联部分两端的电压变大,灯泡A两端的电压变小;

所以灯泡B两端的电压变大,实际功率变大,灯泡变亮;

灯泡A两端的电压变小,实际功率变小,灯泡变暗;

根据欧姆定律可知灯泡C支路的电流减小,实际功率减小,所以灯泡C变暗.

故选C.

阅读理解

阅读理解。

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