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Physics 7B
WS C3 (rev. 2.1)
Page 1
C3. LRC and AC Circuits
Questions for discussion
1
. In an LC circuit
1
, why does the current oscillate?
2.
In an LC circuit, the inductor stores energy in its magnetic field. Likewise, the capacitor stores
energy in its electric field. How do these stored energies vary with time as the circuit oscillates?
How does their
sum
vary with time?
3
. Adding a small resistor to an LC circuit will not change the fact that the current oscillates back
and forth. But the resistor
will
have an important effect on things  what is it?
4.
How do you expect the sum of the stored energies in the capacitor and the inductor to behave in
an LRC circuit? Does this violate conservation of energy?
5
. Consider a simple AC circuit containing a resistor, a capacitor, an inductor, and a sinusoidal
voltage source, all in series.
a)
Why does the inductor cause the amplitude of the current going through this circuit to be small
when the AC frequency is very high?
1
Some problems in LC and LRC circuits require solutions to differential equations. For the results you will
need, and derivations of those results, see “Differential Equations for Circuit Problems” in the Supplementary
Material at the end of the workbook, in the section “LRC Equations.”
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 Fall '10
 yildiz
 Physics, Energy

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