Physics 116A NotesFall 2004David E. PellettDraft v.0.9• Notes Copyright 2004 David E. Pellett unless stated otherwise.• References:– Text for course:Fundamentals of Electrical Engineering, second edition, by LeonardS. Bobrow, published by Oxford University Press (1996)– Others as noted1Physics 116A, 10/20/04: Outline• Types of capacitors and how to read values (handout provided Friday)• Demo of oscilloscope measurement of voltage and phase difference• Phasors (introduction)2Phasors• Phasor: a representation of an AC quantity at a given ω as a magnitude(or amplitude) A and initial phase angle φ, without the ejωtterm (whichcancels in an equation involving AC analysis anyway).• Text uses upper case bold face letters for phasors• Phasors are complex numbers, usually expressed in polar form, just notfunctions of t– remember that vector addition (or more properly, complex numberaddition) is required to add phasors• You can put the time dependence back in by multiplying by ejωtwhereappropriate (or find the real part as fcn of t as A cos(ωt + φ))• Example (capacitor driven by v (t) = V0ejωt):i(t) = v(t)/ZC= jωCV0ejωt= ωCV0ejπ2ejωt• Current expressed as phasor (text uses upper case bold face letters forphasor variables):I = ωCV0690◦• And the actual time-dependent current is i(t) = ωCV0cos(ωt +π2)3Phasors (continued)• The circuit and phasor diagram are shown above– We say I leads V = V060 by 90◦here– If I is considered the output, then this is called a lead network– Compare with results if C is replaced with R or L∗ With R, I and V in phase; With L, I lags V by 90◦• Text refers to phasor analysis as working in the frequency domain– The analysis assumes sinusoids at a single ω (or f ≡ω2π)– The only dependence left is on ω (or f)– Bode plot shows amplitude and phase response as fcn of ω (or
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