问题 选择题

如图甲所示的电路中,电源电压保持4.5V不变,电压表量程为“0~3V”,电流表量程为“0~0.6A”,灯泡上标有“6V,0.5A”字样。闭合开关,将滑片P滑到某—位置时,电压表和电流表的示数如图乙所示。则下列说法错误的是

A.灯泡正常发光时的电阻为12Ω

B.灯丝的电阻随温度的升高而增大

C.此时灯泡的电阻为10Ω

D.此时灯泡的电阻为8.75Ω

答案

答案:D

题目分析:首先根据电路图分析电路的连接方式,根据灯泡铭牌计算灯泡正常发光时的电阻,然后读取电压表和电流表的示数结合欧姆定律计算此时灯泡的电阻,同时考虑灯泡的电阻随温度的变化.灯泡和滑动变阻器串联在电路中,电压表测滑动变阻器的电压,电流表测电路电流.电压表的读数为2.1V,电流表的读数为0.24A.根据欧姆定律灯泡正常发光时的电阻为:

R0===12Ω,此时灯泡的电阻为:R1==10Ω灯泡的电阻会随温度的升高而增大.所以A,B,C不合题意.故选D.

阅读理解

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单项选择题