电路如图：是某一程序控制电路,要求当继电器J1,接点闭合后,输出电压：uab=1/2u,J1,J2接点同时闭合后,uab=1/3u,求R1和R2的值。 
正确答案:
uR1/(1+R1)=1/2u
2R1=1+R1 R1=1KΩ
当J1,J2接点同时闭合：
u=(1+R2×1/(1+R2))I
u=(1+2R2)I/(1+R2).....(a)
1/3u=r2I/(1+r2).......(b)
(a)/(b) 3=(1+2R2)/R2 R2=1KΩ
2R1=1+R1 R1=1KΩ
当J1,J2接点同时闭合：
u=(1+R2×1/(1+R2))I
u=(1+2R2)I/(1+R2).....(a)
1/3u=r2I/(1+r2).......(b)
(a)/(b) 3=(1+2R2)/R2 R2=1KΩ
答案解析:有
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