Lecture 12 Electromagnetic Oscillations and Alternating Current Chp. 33

1
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

2

Axis of rotation
Coil of wire
Where w is the rotational angular frequency of
the generator
w 2pf and f 60 Hz
3
phase
Instantaneous voltage
time
Phase constat
Amplitude
Angular frequency
Phasor diagram
4

L 4.22mH
VRRI
VL XLIL or VL (Lw)I since IIL
5
Impedance Z New quantity for AC circuits. This
is analogous to resistance in DC circuits
6
RL Circuit Example
Suppose em 100 volts, f1000 Hz, R10 Ohms,
L4.22 mH, Find XL, Z, I, VR, and Vl.
7
Power in AC circuits
Instantaneous power doesnt mean anything
Need to average over time or one period of the
sine wave
Note
8
Averaging over a sine curve
9
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
10
Series LRC circuit
VR
VC
XC1/(wC)
VL
XLwL
ELI the ICE man
11
Resonance
Series LRC demo
12
10 uF
4.25 mH
13
Series LCR circuit