2s后,
流过R2的电流i2=uc/R2
流过电容的电流还是ic=Cduc/dt
流过R1的电流=ic十i2
uc=u-(ic十i2)R1
=u-R1Cduc/dt-R1uc/R2
R1Cduc/dt=u-(1十R1/R2)uc
duc/[ u-(1十R1/R2)uc ]=dt/R1C
(-R2/R1)ln[ u-(1十R1/R2)uc ]=t/R1C十F1
ln[ u-(1十R1/R2)uc ]=(-R1/R2)t/R1C十F2
=-t/R2C十F2
u-(1十R1/R2)uc=F3e^(-t/R2C)
uc=[u- F3e^(-t/R2C) ]/ (1十R1/R2)
= R2[u- F3e^(-t/R2C) ]/ (R1十R2)
用戴维南定理可以么
追答这里的t,从2s开始计时,换成从第一个开关合上开始计时,t换成t-2
uc=R2[u-F3e^(-(t-2)/R2C)]/(R1十R2)
t=2,uc=u-ue^(-2/R1C)
=R2[u-F3]/(R1十R2)
u-F3=u(R1十R2)/R2[1-e^(-2/R1C)]
F3=u{1- (R1十R2)/R2[1-e^(-2/R1C)] }
= u{1- (R1十R2)/R2十(R1十R2)/R2× e^(-2/R1C) }
= u{- R1/R2十(R1十R2)/R2× e^(-2/R1C) }
uc=u{1-[-R1/R2十(R1十R2)/R2×e^(-2/R1C)]e^[-(t-2)/R2C]}
t→∞
uc→ uR2/(R1十R2)
最后uc还要乘R2/(R1十R2)
追问谢谢谢