【精品】2021年中考物理电学满分训练15讲：第7讲 欧姆定律四（电路故障及滑动变阻器作用）（原卷版和解析版）
【内容简介】1．掌握常见电路故障分析及处理办法2．掌握滑动变阻器在实际情况中的运用 【经典例题一】1．如图所示，当开关闭合时，灯L1、L2都不亮，电流表无示数，但电压表示数较大。可能的故障是（ ） A．L1断路B．L2断路C．L2短路D．L1短路【解答】解：根据电路可知，灯L1、L2串联，电流表测电路电流，电压表测L2两端电压；开关闭合后，灯L1、L2都不亮，电流表无示数，说明电路断路；电压表示数较大，说明电压表的正负接线柱与电源两极相连，故故障为L2断路。故选：B。2．如图所示电路中闭合开关后，电路正常工作，一段时间后，灯泡突然熄灭，且一个电表示数变大，另一个电表示数变小，小明提出了如下可能的故障：①灯泡L开路；②灯泡L短路；③电阻R开路； ④电阻R短路。请你分析故障可能是（ ） A．①③B．②④C．②③D．③【解答】解：（1）若灯泡L开路，电流表无示数，电压表也无示数，所以两表示数都减小，灯泡不发光，故①不符合题意；（2）若灯泡L短路，则电流表有示数，电压表也有示数，所以两表示数都变大，灯泡不发光，故②不符合题意；（3）若电阻R开路，则电流表无示数，电压表有示数，所以一个表示数变大，一个表示数变小，灯泡不发光，故③符合题意；（4）若电阻R短路，则电流表有示数，电压表无示数，一个表示数变大，一个表示数变小，但灯泡仍发光，故④不符合题意；综上所述：故障可能是电阻R开路引起的。故选：D。【变式练习】1．如图所示，闭合开关S后，灯泡L没有发光，电流表和电压表的示数均为0．若电路中只有一处故障，则可能的故障是（ ） A．灯泡L断路B．电阻R断路C．灯泡L短路D．电阻R短路【解答】解：闭合开关S，发现灯不发光，且电压表示数、电流表示数均为零。电路中一定有断路，故CD错误，可能是电流表断路；小灯泡断路；开关断路；若电阻R断路电压表有示数，故B错误，A正确；故选：A。2．如图所示的电路中，电源两端的电压保持不变，当开关S闭合后，灯L不发光，电压表指针有明显偏转。若电路中只有一处故障，对于此电路可能故障的判断，下列说法中正确的是（ ） A．灯L断路B．R1短路C．R2短路D．灯L短路【解答】解：A、如果灯泡L断路，整个电路断路，灯泡不亮，电压表指针不偏转。故A错误；B、如果R1短路，R1相当于导线，滑动变阻器完好，有电流通过灯泡，所以灯泡能够发光。故B错误；C、如果滑动变阻器R2短路，R2相当于导线，定值电阻完好，有电流通过灯泡，所以灯泡能够发光。故C错误；D、如果灯泡L短路，闭合开关灯泡不会发光，电压表测量电源电压，电压表指针偏转。故D正确。故选：D。3．如图所示的实验电路中，闭合开关，移动滑动变阻器的滑片，发现电压表有示数但无明显变化，电流表有示数并且有变化，小灯泡不亮。则可能的故障原因是（ ）
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