8.
A series RLC circuit has R = 1.200Ω, L = 220.0mH, C = 12.00μF. What fraction of its
original maximum charge does the capacitor attain after one cycle?
(1) 0.9725
(2) 0.9925
(3) 0.9825
(4) 0.9625
(5) 0.9993
In RLC circuits, the capacitor equation for charge becomes
( 29
2
cos
Rt
L
q
Qe
t
ϖ
φ

=
+
The most troublesome thing about this equation is the
( 29
cos
t
+
. Fortunately, we
know that the maximum charge would come when
( 29
cos
1
t
+
=
. And after a
“complete cycle” of the wave, we know that the cosine would return to its original
value, which is also 1. Thus, the equation reduces to
2
Rt
L
q
Qe

=
A “cycle” represents the time. It can be found from the equation for natural frequency,
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This note was uploaded on 05/17/2011 for the course PHY 2049 taught by Professor Any during the Spring '08 term at University of Florida.
 Spring '08
 Any
 Physics, Charge

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