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PRS: LC Circuit
Consider the LC circuit at
right. At the time shown the
current has its ~
value. At this time
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0% ~ The charge 00 the capacitor has its maximum value""" 11\ It). }LJt
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0% The eleclrlc field has its maximum value .-!!JIt{1
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0% 4. The charge on the capaCitor IS zero
0% . Don't have a clue
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PRS: LC Circuit
In the LC circuit at right the e
current is in the direction
==
shown and the charges on
the capacitor have the signs F
shown. At this time,
-Q +Q
:r
0% @ I is increasing and Q is increasing
0% I is increasing and Q is decreasing
0% 3. I is decreasing and Q is increasing
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4. I is decreasing and Q is decreasing
5. Don't have a clue
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PRS Answer: LC Circuit
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Answer: 4. The current is
maximum when the charge
on the capacitor is zero
Current and charge are exactly 90 degrees out of
phase in an ideal LC circuit (no resistance). so when
the current is maximum the charge must be
identically zero.
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PRS Answer: LC Circuit
Answer: 2. I is increasing;
Q is decreasing
With current in the direction
shown, the capacitor is
discharging (Q is decreasing).
But since Q on the right plate is positive, I must be
increasing. The positive charge wants to flow, and
the current will increase until the charge on the
capacitor changes sign. That is, we are in the first
quarter period of the discharge of the capacitor,
when Q is decreasing and positive and I is
increasing and positive.
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PRS: LC Circuit
The plot shows the charge ' ..... =-.---,="
on a c~ r (black curve) ~ .
and the current through it
(red curve) after you turn
off the power supply. If yOU ! 4J
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PRS Answer: LC Circuit
Answer:
1. T Lag will increase 11 ..... '
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Putting in a core increases the inductor's
inductance and hence decreases the natural
frequency of the circuit. Lower frequency means
longer period. The phase will remain at 90' (a
quarter period) so T lag will increase.
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