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Unformatted text preview: Chapter 35: AC Cir cuits (Knight: 35.13) B x . F F θ θ μ B U • = μ B × = μ τ AI = μ Physics 113 Dr. Renat Letfullin 2 Today... • AC Sources and Phasors • Resistor Circuits – Examples • Capacitor AC Circuits (1) – Capacitive Reactance – Examples • Voltage Dividers • Analyzing a RC Circuit • Filters and Transmission Physics 113 Dr. Renat Letfullin 3 AC Sour ces and Phasor s You can think of an AC generator as a batterylike object with an emf that varies sinusoidally as E (t) = E cos ϖ t , where E 0 is the maximum emf and ϖ is the angular frequency, with ϖ =2 π f , where f is the frequency in Hz. Alternatively, the emf and other oscillatory quantities can be represented by a phasor diagr am . The phasor is a vector of length E that rotates counterclockwise around the origin with angular frequency ϖ , so that the angle it makes with the horizontal axis at any time is ϖ t . The projection of the phasor on the horizontal axis at any time gives the emf. Physics 113 Dr. Renat Letfullin 4 Clicker Question 1 The instantaneous value of the emf E represented by this phasor is: (a) I ncreasing; (b) Decreasing; (c) Constant; (d) I t is not possible to tell without knowing t . Physics 113 Dr. Renat Letfullin 5 Resistor Cir cuits Consider an AC current i R through a resistor. Ohm’s Law gives the potential drop across the resistor, which we will call the r esistor voltage v R . R R v i R = I f the resistor is connected in an AC circuit as shown, then Kirschoff’s loop law tells us that: soruce R R V V v ∆ + ∆ = =E ( ) cos R t t v ϖ = = E E cos cos R R R v i t I t R R ϖ ϖ = = = E I n the phasor diagram, the phasors for v R and i R are parallel. Physics 113 Dr. Renat LetfullinDr....
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This note was uploaded on 03/08/2009 for the course PH 113 taught by Professor Joenathan during the Fall '08 term at RoseHulman.
 Fall '08
 JOENATHAN
 Physics, Magnetism

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