Discussion Question 11C
Physics 212 week 11
RLC Preview
1
You will learn much more about RCL circuits in the next lecture but here is a preview of their
interesting behavior.
In this circuit, an initial charge of
Q
0
=1
µ
C
is placed on the capacitor.
At time t=0 the switch is closed.
The charge on the capacitor oscillates
while dying out as shown below:
Our conventions are that
I
is positive when flowing in the direction of the arrow, and Q is
positive when the top plate of the capacitor is positive and the bottom plate is negative as
illustrated.
(a) Immediately after the switch is thrown, what is the current
I
(0
+
)?
Right before the switch is thrown I = 0 .The inductor resists an immediate change in current
so the current will be 0 immediately after the switch is thrown.
(b) Immediately after the switch is thrown, what is the voltage drop across the inductor, and what
is the rate of change of current or
dI/dt
(0
+
) ?
Hints
:
What is the voltage drop across the
capacitor? What must the voltage drop across the inductor be according to KVL?
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 Spring '08
 Kim
 Charge, Magnetism

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