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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 • 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
Impedance Z: New quantity for AC circuits. This is analogous to resistance in DC circuits
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
Series LRC circuit VR VC XC=1/(wC) VL XL=wL ELI the ICE man
Resonance Series LRC demo
10 uF 4.25 mH