UT PHYS 2080 - Chapter 21 Alternating Current Circuits

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Chapter 21AC CircuitsElectromagnetic WavesAC CircuitResistor in an AC CircuitResistor, Cont.More About Resistors in an AC Circuitrms Current and Voltagerms GraphPower RevisitedNotation NoteOhm’s Law in an AC CircuitCapacitors in an AC CircuitCapacitors, Cont.More About Capacitors in an AC CircuitCapacitive Reactance and Ohm’s LawInductors in an AC CircuitSlide 18Inductive Reactance and Ohm’s LawThe RLC Series CircuitCurrent and Voltage Relationships in an RLC Circuit, Graphical SummaryPhasor DiagramsPhasor Diagram for RLC Series CircuitPhasor Diagram, Cont.ΔVmax From the Phasor DiagramImpedance of a CircuitImpedance and Ohm’s LawSummary of Circuit Elements, Impedance and Phase AnglesNikola TeslaProblem Solving for RLC CircuitsProblem Solving, Cont.Power in an AC CircuitPower in an AC Circuit, Cont.Resonance in an AC CircuitResonance, Cont.TransformersTransformers, 2Transformers, 3Transformer, FinalElectrical Power TransmissionJames Clerk MaxwellMore of Maxwell’s ContributionsMaxwell’s Starting PointsMaxwell’s PredictionsHeinrich Rudolf HertzHertz’s Basic LC CircuitLC Circuit, Cont.Hertz’s Experimental ApparatusHertz’s ExperimentHertz’s ConclusionsHertz’s Measurement of the Speed of the WavesElectromagnetic Waves Produced by an AntennaEM Waves by an Antenna, Cont.EM Waves by an Antenna, FinalCharges and Fields, SummaryElectromagnetic Waves, SummaryElectromagnetic Waves are Transverse WavesProperties of EM WavesProperties of EM Waves, 2Properties of EM Waves, 3Properties of EM Waves, FinalDetermining Radiation PressureProperties of EM Waves, SummaryThe Spectrum of EM WavesThe EM SpectrumNotes on The EM SpectrumNotes on the EM Spectrum, 2Notes on the EM Spectrum, 3Notes on the EM Spectrum, FinalCrab Nebula in Various WavelengthsDoppler Effect and EM WavesDoppler Equation for EM WavesDoppler Equation, Cont.Chapter 21Alternating Current Circuits and Electromagnetic WavesAC Circuits•AC circuits power everyday electric appliances.•Will look at various circuit elements in an AC circuit–Resistor–Capacitor–Inductor•Also will look at what happens when these elements are placed in combinations in AC circuitsIntroductionElectromagnetic Waves•Electromagnetic waves are composed of fluctuating electric and magnetic fields.•Electromagnetic waves come in various forms.–These forms include•Visible light•Infrared•Radio•X-raysIntroductionAC Circuit•An AC circuit consists of a combination of circuit elements and an AC generator or source.•The output of an AC generator is sinusoidal and varies with time according to the following equation–Δv = ΔVmax sin 2ƒt•Δv is the instantaneous voltage•ΔVmax is the maximum voltage of the generator•ƒ is the frequency at which the voltage changes, in HzSection 21.1Resistor in an AC Circuit•Consider a circuit consisting of an AC source and a resistor.Section 21.1Resistor, Cont.•The graph shows the current through and the voltage across the resistor.•The current and the voltage reach their maximum values at the same time.•The current and the voltage are said to be in phase.Section 21.1More About Resistors in an AC Circuit•The direction of the current has no effect on the behavior of the resistor.•The rate at which electrical energy is dissipated in the circuit is given by– P = i² R•Where i is the instantaneous current•The heating effect produced by an AC current with a maximum value of Imax is not the same as that of a DC current of the same value.•The maximum current occurs for a small amount of time.Section 21.1rms Current and Voltage•The rms current is the direct current that would dissipate the same amount of energy in a resistor as is actually dissipated by the AC current.•Alternating voltages can also be discussed in terms of rms values.Section 21.1rms Graph•The average value of i² is ½ I²maxSection 21.1Power Revisited•The average power dissipated in resistor in an AC circuit carrying a current I is– Pav = I²max RNotation NoteSection 21.1Ohm’s Law in an AC Circuit•rms values will be used when discussing AC currents and voltages.–AC ammeters and voltmeters are designed to read rms values.–Many of the equations will be in the same form as in DC circuits.•Ohm’s Law for a resistor, R, in an AC circuit–ΔVR,rms = Irms R•Also applies to the maximum values of v and iSection 21.1Capacitors in an AC Circuit•Consider a circuit consisting of an AC source and a capacitor.Section 21.2Capacitors, Cont.•The current starts out at a large value and charges the plates of the capacitor.–There is initially no resistance to hinder the flow of the current while the plates are not charged.•As the charge on the plates increases, the voltage across the plates increases and the current flowing in the circuit decreases.Section 21.2More About Capacitors in an AC Circuit•The current reverses direction.•The voltage across the plates decreases as the plates lose the charge they had accumulated.•The voltage across the capacitor lags behind the current by 90°Section 21.2Capacitive Reactance and Ohm’s Law•The impeding effect of a capacitor on the current in an AC circuit is called the capacitive reactance and is given by–When ƒ is in Hz and C is in F, XC will be in ohms•Ohm’s Law for a capacitor in an AC circuit–ΔVC,rms = Irms XCSection 21.2Inductors in an AC Circuit•Consider a circuit consisting of an AC source and an inductor.Section 21.3Inductors in an AC Circuit•The current in the circuit is impeded by the back emf of the inductor.•The voltage across the inductor always leads the current by 90°Section 21.3Inductive Reactance and Ohm’s Law•The effective resistance of a coil in an AC circuit is called its inductive reactance and is given by–XL = 2ƒL•When ƒ is in Hz and L is in H, XL will be in ohms•Ohm’s Law for the inductor–ΔVL,rms = Irms XLSection 21.3The RLC Series Circuit•The resistor, inductor, and capacitor can be combined in a circuit.•The current in the circuit is the same at any time and varies sinusoidally with time.Section 21.4Current and Voltage Relationships in an RLC Circuit, Graphical Summary•The instantaneous voltage across the resistor is in phase with the current.•The instantaneous voltage across the inductor leads the current by 90°•The instantaneous voltage across the capacitor lags the current by 90°Section 21.4Phasor Diagrams•To account for the different phases of the voltage


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UT PHYS 2080 - Chapter 21 Alternating Current Circuits

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