Lecture 31b - Chapter 31 Simple AC circuits Resistor circuits =msint Notation Use lowercase for instantaneous values Uppercase for peak values vR =

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Chapter 31: Simple AC circuits
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RR V I R Resistor circuits Notation: Use lowercase for instantaneous values, Uppercase for peak values v R = ε = V R sin ωt i R = v R /R = I R sin ωt In an AC circuit, resistor voltage and current oscillate in phase . ε=ε m sinωt
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Capacitor circuits v C = ε = V C sin ωt i = dq/dt and q = Cv C : i C = ωCV C cos ωt which we write as: i C = ωCV C sin (ωt + π/2) The current leads voltage by π/2 rads ICE ε=ε m sinωt Current reaches peak value I C the instant the capacitor is fully discharged and v C =0. The current is zero the instant the capacitor is fully charged.
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Capacitive Reactance – Relationship between peak current and voltage in a capacitor I C = ωCV C , although they don’t happen at the same time. Define the capacitive reactance X C = 1/ ωC, then: I C = V C /X C This is analogous to Ohm’s Law for DC. at very high frequencies, X C approaches 0 and the capacitor acts like a wire. Units of X C :
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Consider this circuit. The frequency of the AC source is adjusted, while its voltage amplitude is kept constant.
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This note was uploaded on 02/05/2011 for the course PHYS 220B taught by Professor Preminger during the Fall '10 term at CSU Northridge.

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Lecture 31b - Chapter 31 Simple AC circuits Resistor circuits =msint Notation Use lowercase for instantaneous values Uppercase for peak values vR =

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