phy22 - Chapter 21 Alternating Current Circuits and...

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1 Chapter 21 Alternating Current Circuits and Electromagnetic Waves 21.1 Resistors in an AC circuit AC circuit ac power source V = V max sin(2 ft) It changes with time t. f is the frequency (60 Hz in the US, Canada and a few other countries with close ties to the US; 50Hz in Europe and most other countries) All powers we see on things (e.g., light bulbs) are average powers : P av = i 2 R = ½ (I max ) 2 R
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2 V rms = I rms R V max = I max R i R =v R R R is a constant for all frequencies V rms = I rms X C , or I rms = V rms /X C X C : Capacitive Reactance fC X C 2 1 Unit: ( ) 21.2 Capacitors in an AC circuit v lags i by 90 o Early
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3 21.3 Inductors in an AC circuit V rms = I rms X L X L : Inductive Reactance fL X L 2 •The higher the frequency, the higher the resistance • Hard for current to go through and deal with self inductance at the same time •Current lags v Unit: v leads i by 90 o 21.4 RLC Circuit • The voice you hear from your cell phone is from this circuit; same is true for all other wireless signals • Current is the same for all components (in series).
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phy22 - Chapter 21 Alternating Current Circuits and...

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