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Lecture 11 Electromagnetic Oscillations and
Alternating Current Chp. 31
• Warm-up problem
• Topics
– Transformers
– LC Circuit Qualitatively
– Electrical and Magnetic energy oscillations
– Alternating current
– Pure R and L circuits
– Series RLC circuit
– Power and Transformers
• Demos
dAnBm
ˆ!=•
!"
AdB!!
!=
dAB !cos=
!
n̂
B
�
! = "d#
dt= "
d(BAcos$)
dt= "BA
dcos$
dt= BAsin$
d$
dt
= BA% sin$ but $ = %t so d$
dt= %
�
! = BA" sin"t
�
! = !msin"t
Where " is the rotational angular
frequency of the generator"= 2#f and f= 60 Hz
Axis of rotationCoil of wire
Driven RLC Series Circuit
1.0 uF 4.25 mH
f =1
6.28 LC=
1
6.28 4.25 !10"3H !10
"6F
f = 2445Hz
Demonstration
Series LCR circuit
P=Irms
2R
Effective Power
Irms=I
2
rms=root-mean-square
Peak value
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