Transcript Document
Physics 121: Electricity &
Magnetism – Lecture 13
Carsten Denker
NJIT Physics Department
Center for Solar–Terrestrial Research
LC Oscillations
q2
UE
2C
April 18, 2007
UB
1 2
Li
2
1
LC
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LC Oscillations (cont.)
d 2q 1
L 2 q0
dt
C
d 2q
dq 1
L 2 R
q0
dt
dt C
q Q cos t
q Qe Rt / 2 L cos t
Damped Oscillation
q2 Q2
UE
cos 2 t
2C 2C
dq
i
Q sin t
dt
April 18, 2007
q2 Q2
UB
sin 2 t
2C 2C
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Alternating Current/Forced
Oscillations
AC: alternating current
DC: direct current
d: driving angular frequency
Whatever the natural angular
frequency of a circuit may be,
forced oscillations of charge,
current, and potential difference
in a circuit always occur at the
driving frequency d.
April 18, 2007
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Resistive, Capacitive, & Inductive Load
VR I R R
1
XC
d C
VC IC X C
X L d L
VL I L X L
Resistor
April 18, 2007
Capacitor
Inductor
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Series RLC Circuit
April 18, 2007
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Series RLC Circuit (cont.)
Impedance
Z R X L XC
2
m
m
Current
amplitude
I
Phase constant
X L XC
tan
R
Resonance
April 18, 2007
Z
d
2
R d L 1/ d C
2
1
LC
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2
Power in Alternating–Current Circuits
I
2
RMS current
I rms
RMS voltage
Vrms
RMS EMF
rms
Average power
2
Pavg Irms
R
V
2
2
Pavg rms Irms cos
April 18, 2007
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Transformers
Transformation of voltage
Ns
Vs Vp
Np
Transformation of currents
Is I p
Np
Ns
Load resistance
Step–up transformer
Step–down transformer
April 18, 2007
2
Np
Req
R
Ns
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