Question

如图所示,已知R1=30欧姆,R2/R3=1/2,当开关S闭合时,V的读数是U1,S断开时,V的读数是U2,且U1/U2

Answer 1

闭合时,R1,R2串联,测得是R2 上的电压

U1=E/(R1+R2)*R2

断开时,三个电阻串联,测得是R2+R3的电压

U2=E/(R1+R2+R3)*(R2+R3)=E/(R1+3R2)*3R2

U1:U2=R2/(R1+R2):3R2/(R1+3R2)=(30+3R2):3(30+R2)=(10+R2):(30+R2)=1:2

R2=10欧姆

R3=20欧姆