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Physics 208N-004 Lecture #25
– 21 March 2011
Chapter 25: 7 AC
and 30: 7-9 – AC Circuits
Review
LC
Circuits and Electromagnetic Oscillations
.
Loop Rule
Harmonic Oscillator
Energy
LCR Circuit
The system will be underdamped for
R
2
< 4
L
/
C
, and
overdamped for
R
2
> 4
L
/
C
.
Critical damping will occur when
R
2
= 4
L
/
C
.
.
.
Underdamped

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Current from a battery flows
steadily in one direction
(direct current, DC). Current
from a power plant varies
sinusoidally (alternating
current, AC).
25-7 Alternating Current
The voltage varies sinusoidally with time:
,
as does the current:
Multiplying the current and the voltage gives the
power:
25-7 Alternating Current
Usually we are interested in the average power:
.