作业帮求解一道物理题?第8题
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求解一道物理题?第8题
求解一道物理题?第8题
求解一道物理题?第8题
²表示平方；/表示分数号
将R1看做R3和R4两个电阻,R3+R4=R1＞R0,其中R3由小变大,从0增大到R1,R4=R1-R3
R2和R3先并联,然后再与R0和R4串联
R2与R3并联的电阻值R'=R2R3/(R2+R3)
R2的分压值：
U’ = U[R2R3/(R2+R3)] / [R2R3/(R2+R3)+R0+R4]
= U[R2R3/(R2+R3)] / [R2R3/(R2+R3)+R0+R1-R3]
= UR2R3 / [R2R3+(R0+R1-R3)(R2+R3)]
= UR2R3 / [R0R2+R1R2+(R0+R1)R3-R3²]
电流表A1的读数：
I1 = U'/R3 = UR2 / [R0R2+R1R2+(R0+R1)R3-R3²]
f(R3)=-R3²+(R0+R1)R3+R0R2+R1R2开口向下,对称轴R3=(R0+R1)/2
R3＜(R0+R1)/2时,f(R3)单调增,I1单调减；R3＞(R0+R1)/2时,f(R3)单调减,I1单调增.
∴C选项正确
电流表A2的读数：
I2 = U'/R2 = UR3 / [R0R2+R1R2+(R0+R1)R3-R3²] = U / [(R0+R1)+(R0+R1)R2/R3-R3]
(R0+R1)R2/R3单调减,并且R3单调增；∴[(R0+R1)+(R0+R1)R2/R3-R3单调增,∴I2 单调减
∴B选项正确
综上,B、C选项正确