# Lecture 12 Electromagnetic Oscillations and Alternating Current Chp. 33 - PowerPoint PPT Presentation

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Lecture 12 Electromagnetic Oscillations and Alternating Current Chp. 33. Cartoon -. Opening Demo - Warm-up problem Physlet Topics LC Circuit Qualitatively Electrical and Magnetic energy oscillations Alternating current \Pure R and L, circuti Series RLC circuit Power and Transfomers

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Lecture 12 Electromagnetic Oscillations and Alternating Current Chp. 33

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### Lecture 12 Electromagnetic Oscillations and Alternating Current Chp. 33

• Cartoon -. Opening Demo - Warm-up problem

• Physlet

• Topics

• LC Circuit Qualitatively

• Electrical and Magnetic energy oscillations

• Alternating current

• \Pure R and L, circuti

• Series RLC circuit

• Power and Transfomers

• Demos

• LR circuit

• Series LRC circuit

B

Axis of rotation

Coil of wire

Where w is the rotational angular

frequency of the generator

w= 2pf and f= 60 Hz

phase

Instantaneous voltage

time

Phase constat

Amplitude

Angular frequency

Phasor diagram

L = 4.22mH

VR=RI

VL= XLIL or VL= (Lw)Isince I=IL

### RL Circuit Example

Suppose em = 100 volts, f=1000 Hz, R=10 Ohms, L=4.22 mH,

Find XL, Z, I, VR, and Vl.

### Power in AC circuits

Instantaneous power doesn’t mean anything

Need to average over time or one period of the sine wave

Note

### Calculate Power lost in resistor from example

To calculate power produced by the generator you need to take account of the phase difference between the voltage and the current. In general you can write:

For an inductor P = 0 because the phase difference between current through the inductor and voltage across the inductor is 90 degrees

VR

VC

XC=1/(wC)

VL

XL=wL

ELI the ICE man

Series LRC demo

10 uF

4.25 mH