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Electromagnetism- AC circuits

Electromagnetism- AC circuits - Chapter 35 AC...

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Chapter 35: AC Circuits (Knight: 35.1-3) B x . F F θ θ μ B U - = μ B × = μ τ AI = μ
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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
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Physics 113 Dr. Renat Letfullin 3 AC Sources and Phasors You can think of an AC generator as a battery-like object with an emf that varies sinusoidally as E (t) = E 0 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 diagram . The phasor is a vector of length E 0 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.
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Physics 113 Dr. Renat Letfullin 4 Clicker Question 1 The instantaneous value of the emf E represented by this phasor is: (a) Increasing; (b) Decreasing; (c) Constant; (d) It is not possible to tell without knowing t .
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Physics 113 Dr. Renat Letfullin 5 Resistor Circuits Consider an AC current i R through a resistor. Ohm’s Law gives the potential drop across the resistor, which we will call the resistor voltage v R . R R v i R = If the resistor is connected in an AC circuit as shown, then Kirschoff’s loop law tells us that: 0 soruce R R V V v + ∆ - = =E 0 ( ) cos R t t v ϖ = = E E 0 cos cos R R R v i t I t R R ϖ ϖ = = = E In the phasor diagram, the phasors for v R and i R are parallel.
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Physics 113 Dr. Renat Letfullin 6
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