lecture 21 - Chapter 21 Alternating Current Circuits and...

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    Chapter 21 Alternating Current Circuits  and Electromagnetic Waves
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    AC 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 = ΔV max  sin 2 π ƒt Δv is the instantaneous voltage ΔV max  is the maximum voltage of the generator ƒ is the frequency at which the voltage changes, in Hz
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    Resistor in an AC Circuit Consider a circuit  consisting of an AC  source and a resistor 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
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    More 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   where i is the  instantaneous current the heating effect produced by an AC current with a  maximum value of I max  is not the same as that of a DC  current of the same value The maximum current occurs for a small amount of time 2 i R ℘ =
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    rms 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 max max 0.707 2 rms I I I = = max max 0.707 2 rms V V V = =
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    Power Revisited The average power dissipated in  resistor in an AC circuit carrying a  current I is   2 av rms I R =
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    Ohm’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 ΔV R,rms  = I rms  R Also applies to the maximum values of v and i
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    Capacitors in an AC Circuit Consider a circuit containing a capacitor and  an AC source 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
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    More About Capacitors in an  AC Circuit The current reverses  direction The voltage across the  plates decreases as the 
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This note was uploaded on 09/06/2009 for the course PHYSICS Physics 2A taught by Professor Sydney.sukuta during the Fall '09 term at San Jose City College.

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lecture 21 - Chapter 21 Alternating Current Circuits and...

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