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PHY2061
R. D. Field
Department of Physics
chp31_4.doc
University of Florida
Charging a Capacitor
After the switch is closed the current is
entering the capacitor so that
I = dQ/dt
,
where
Q
is the charge on the capacitor
and
summing all the potential changes in
going around the loop gives
ε
−−=
IR
Q
C
0
,
where
I(t)
and
Q(t)
are a function of time.
If the switch is closed at t=0 then
Q(0)=0
and
−−
=
R
dQ
dt
Q
C
0
,
which can be written in the form
()
QC
=−
−
1
τ
,
where I have define
τ
=RC
.
Dividing by (Q
ε
C) and multiplying by dt and integrating gives
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This note was uploaded on 05/31/2011 for the course PHY 2061 taught by Professor Fry during the Spring '08 term at University of Florida.
 Spring '08
 FRY
 Physics, Charge, Current

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