电压表与R2并联,R2与R1串联,电流表测R1的.

题目

电压表与R2并联,R2与R1串联,电流表测R1的.
R1=30欧,R2电阻丝最长时,R2电压为4.5V,当P在R2的中点时,R2电压为3V（1）电源电压（2）R2的总电阻（3）P在两个位置时,电流表的示数.
!!!!R1是 30欧

答案

(U-4.5)/4.5=R1/R2 (U-3)/3=R1/(R2/2) 二式相比,得:(U-4.5)/(U-3)=3/4 可解得,电源电压为:U=9V 则由(U-4.5)/4.5=R1/R2,得 R2=R1*4.5/(U-4.5)=30*4.5/(9-4.5)=30欧 P在R2的最大电阻处时,I=4.5/R2=4.5/30=0.15A P在R2...