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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 Generators October 11 Physics 104, Fal 2009 2 v v r Flux is decreasing at moment shown x 2 Generators and EMF 1 = B L v sin( ) v = r October 11 Physics 104, Fal 2009 3 v v r = w/2 1 = r B L sin( ) = 2 = 1 + 2 = 2 r B L sin( ) t 1 AB AB Two of the sides (width w) do not contribute but two with lengths (L) do N loops: = NAB sin( t) = A B sin( ) = A B sin( t) x Generators and EMF October 11 Physics 104, Fal 2009 4 x = A B sin( ) x x 1 2 3 At which time does the loop have the greatest emf? 1) Has greatest flux, but = 0 so = 0. 2) Part way, 30 so AB/2. 3) Flux is zero, but = 90 so = AB. 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 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 ft I = I sin2 ft P = VI = V I sin 2 2 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 f t) V 0 or V max = maximum voltage f = frequency (cycles/second) V(t) = 24 sin(8 t) October 11...
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