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**Unformatted text preview: **Class 14 AC Circuits and electromagnetic Waves Physics 106 Fall 2011 Press CTRL-L to view as a slide show. Learning Outcomes Last time we discussed: I Inductors and self-inductance I RL Circuit Problems I AC Circuit Terminology I R, L, and C in AC Circuits Learning Outcomes Today we will discuss: I The Series RLC Circuit I Power in AC Circuits I Resonance I Transformers I Radiation Phasors and the Series RLC Circuit The RLC Series Circuit I The resistor, inductor, and capacitor can be combined in a circuit I The current in the circuit is the same at any time and varies sinusoidally with time Current and Voltage Relationships in an RLC Circuit I In a series RLC circuit, the voltages across the R, L, and C must add to equal the voltage of the power supply at all times. Phasor Diagram for RLC Series Circuit I Let I = I max sin ( 2 π ft ) . I At time t = 0, the current is 0. I At time t = 0, the current phasor is in the x direction. Phasor Diagram for RLC Series Circuit I The voltage across the resistor is on the + x axis since it is in phase with the current I The voltage across the inductor is on the + y axis since it leads the current by 90 ◦ I The voltage across the capacitor is on the- y axis since it lags behind the current by 90 ◦ Circuit Rules for AC Circuits If two or more circuit elements are in series, they have the same current phasor : Phasor Diagram for RLC Series Circuit I Add voltage phasors (as vectors) to get the total emf Impedance and Phasors I Divide voltages by the current I Z is the "impedance" I V max = I max Z Impedance and Ohm’s Law I Ohm’s Law can be applied to the impedance I V max = I max Z I This can be regarded as a generalized form of Ohm’s Law applied to a series AC circuit Summary of Circuit Elements, Impedance and Phase Angles Power in AC Circuits Power in an AC Circuit I No power lost in C or L I Energy is stored in these fields and drawn back out of fields I Power is only lost in R Power in an AC Circuit I Average Power Loss: P av = I rms V R , rms = I rms V source , rms cos φ I cos φ is called the power factor of the circuit An AC Circuit Problem A Series RLC Circuit A series RLC circuit consists of I 120 Vrms, 60.0 Hz power supply I 5.00 Ω resistor I 200 μ F capacitor I 12.0 mH inductor A Series RLC Circuit A series RLC circuit consists of I 120 Vrms, 60.0 Hz power supply I 5.00 Ω resistor I 200 μ F capacitor I 12.0 mH inductor I What are X L , X C , and Z ?...

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