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Unformatted text preview: 1 Physics 208N004 Lecture #25 – 21 March 2011 Chapter 25: 7 AC and 30: 79 – AC Circuits Review LC Circuits and Electromagnetic Oscillations . Loop Rule Harmonic Oscillator Energy LCR Circuit The system will be underdamped for R 2 < 4 L / C , and overdamped for R 2 > 4 L / C . Critical damping will occur when R 2 = 4 L / C . . . Underdamped 2 Current from a battery flows steadily in one direction (direct current, DC). Current from a power plant varies sinusoidally (alternating current, AC). 257 Alternating Current The voltage varies sinusoidally with time: , as does the current: Multiplying the current and the voltage gives the power: 257 Alternating Current Usually we are interested in the average power: . 3 The current and voltage both have average values of zero, so we square them, take the average, then take the square root, yielding the rootmeansquare (rms) value: 257 Alternating Current Example 2513: Hair dryer. (a) Calculate the resistance and the peak current in a 1000 W hair dryer connected to a 120V line. (b) What happens if it is connected to a 240V line in Britain? Resistors, capacitors, and inductors have different phase relationships between current and voltage when placed in an ac circuit....
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This note was uploaded on 09/18/2011 for the course PY 208M 87878 taught by Professor George during the Spring '09 term at N.C. State.
 Spring '09
 GEORGE

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