Lecture 12 Electromagnetic Oscillations and Alternating Current Chp

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

Axis of rotation Coil of wire w= 2 pf and f= 60 Hz B Where w is the rotational angular frequency of the generator

phase Instantaneous voltage Amplitude time Angular frequency Phasor diagram Phase constat

L = 4. 22 m. H VR=RI VL= XLIL or VL= (Lw)I since 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 m. H, 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

Averaging over a sine curve

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/(w. C) VL XL=w. L ELI the ICE man

Resonance Series LRC demo

10 u. F 4. 25 m. H

Series LCR circuit