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