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Lect10 - 1 Lecture 10 Inductors AC Power Circuits • AC...

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Unformatted text preview: 1 Lecture 10: Inductors, AC Power, Circuits • AC Power – Transformers – Transmission • Inductors – LCR Circuits • Impedance • Resonance October 11 Physics 104, Fal 2009 1 θ Generators October 11 Physics 104, Fal 2009 2 v v ω r Flux is decreasing at moment shown x 2 Generators and EMF ε 1 = B L v sin( θ ) v = ω r October 11 Physics 104, Fal 2009 3 v v θ ω r = w/2 ε 1 = ω r B L sin( θ ) = ε 2 ε = ε 1 + ε 2 = 2 ω r B L sin( θ ) ε t 1 ω AB ¡ ω AB Two of the sides (width w) do not contribute but two with lengths (L) do N loops: ε = NAB ω sin( ω t) ε = A B ω sin( θ ) ε = A B ω sin( ω t) x Generators and EMF October 11 Physics 104, Fal 2009 4 • x ε = ω A B sin( θ ) • x • x 1 2 3 At which time does the loop have the greatest emf? 1) Has greatest flux, but θ = 0 so ε = 0. 2) Part way, θ ≈ 30 so ε ≈ ω AB/2. 3) Flux is zero, but θ = 90 so ε = ω AB. θ Direct versus Alternating Current • Chemical power – Battery – Constant voltage – Constant current • Circular motion – Generator – Sinusoidal time variation October 11 Physics 104, Fal 2009 5 Sinusoidal Pattern • Circular motion – Sinusoidal pattern – Frequency, f – Period, T = 1 / f – Goes through 0 twice in one period October 11 Physics 104, Fal 2009 6 x = x sin2 π ft 2 AC Power • Voltage, current and power depend on time October 11 Physics 104, Fal 2009 7 • We are interested in averages ( f = 60Hz) V = V sin2 π ft I = I sin2 π ft P = VI = V I sin 2 2 π ft I rms = V rms R P ave = V rms I rms = V rms 2 R = I rms 2 R P ave = 1 2 V I V rms = V 2 I rms = I 2 AC Source V(t) = V sin(2 π f t) – V 0 or V max = maximum voltage – f = frequency (cycles/second) • V(t) = 24 sin(8 π t) October 11...
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Lect10 - 1 Lecture 10 Inductors AC Power Circuits • AC...

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