# Lect_42 - RC circuit = circuit with resistors and...

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Lecture 42 RC circuits RC circuit RC circuit = circuit with resistors and capacitors. R C ε The simplest one: Charging the capacitor Capacitor initially uncharged. At t = 0, close the switch. + + –– = 0 + : (right after) = (0) I Current flows “through” C as through an ideal wire (0) 0 Q = +++ ––– At : () 0 ∞= C acts like an open switch () = Charge builds up on the capacitor’s plates, and C Qt Vt = After a long time, and charges cannot move. C V = Adding charge to the plates is more and more difficult. E battery C ( )

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Q t I () 0 ∞= () C ε = (0) R (0) 0 = ACT: Charging a capacitor The capacitor in the circuit below is initially uncharged. What is its charge ( ) a long time after the switch is closed? A. ( ) < ε C B. ( ) = ε C C. ( ) > ε C ε 1 2 C When the capacitor is fully charged and behaves like an open switch, there is still current in this circuit! 1 12 RR = + 2 The potential difference between points A and B is: A B1 2 V VI −=− = B A 2 2 CV CIR ⇒∞ = == < + Charging the capacitor (quantitative) Charging the capacitor (quantitative)
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## This note was uploaded on 04/16/2008 for the course PHYSICS 221 taught by Professor Johnson during the Fall '06 term at Iowa State.

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Lect_42 - RC circuit = circuit with resistors and...

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