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"Nothing in life is to be feared, it is only to be understood." ..."Marie Curie 1867-1934, Polish born French Physicist, Twice Nobel Prize Winner- Physics and Chemistry)"

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 Author Topic: RC circuit (DC: charge/discharge)  (Read 23992 times) 0 Members and 1 Guest are viewing this topic. Click to toggle author information(expand message area).
Fu-Kwun Hwang
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 « Embed this message on: December 14, 2005, 12:22:46 pm » posted from:Taipei,T'ai-pei,Taiwan

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The red dots represent the electrons.
The color of the capacitor is yellow (red+green) to represent neutral charge.
When electron enter one side of the capacitor, color for part of the region turn into red.
Another side of the capacitor lack of electron so it color turn into green.
You can charge the capacitor or discharge it.

For the charging cycle: $V_s=V_R+V_C=I R + \int \frac{I dt}{C}$ where Vs is the voltage from the power supply.
$0=R \frac{dI}{dt}+ \frac{I}{C}$$\frac{dI}{dt}=-\frac{I}{RC}$,  so the solution is $I(t)=I_0 e^{-t/(RC)}$
at $t=0, V_c=0$ so $I(t=0)=I_0=V_s/R$
The result is $V_R(t)=I(t) R =V_s e^{-t/(RC)}$, V_c(t)=V_s-V_R(t)= V_s (1- e^{-t/(RC)})

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