(2011?乐山模拟)用如图甲所示的电路可以测量一个未知电阻的阻值,其中Rx为待测电阻,R为电阻箱(符号为
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(1)根据电路图,连接实物,将电阻箱的阻值调至最大;然后把开关S接a点,读出电流表的示数为I(此电流为Rx、R0共同作用的效果);再把开关S接b点,调节电阻箱,使电流表的示数仍变为原来的数值I(此电流为R、R0共同作用的效果);最后读出电阻箱的示数R.故答案为:DCAB.
(2)根据图乙中左下角的指针位置可知,4×10=40Ω;根据图乙中右下角的指针位置可知,7×1=7Ω.
由此可知,步骤A中电阻箱调节好后示数为40Ω+7Ω=47Ω;
因为Rx和R0共同作用的效果与R、R0共同作用的效果相同,
所以Rx+R0=R+R0,即Rx=R=47Ω.
故答案为:47;47.
(3)Rx和R0共同作用的效果与R、R0共同作用的效果相同,则Rx+R0=R+R0,即Rx=R.
这里用电阻箱R等效替代了待测电阻Rx.
故答案为:等效替代法.
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