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PHY122_L13forPostingByPMK

PHY122_L13forPostingByPMK - PHY122 Physics for the Life...

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PHY122 – Physics for the Life Sciences II Lecture 13 AC Electricity Resistors, Capacitors, and Inductors Question: How are we doing on right-hand rules? Thumbs up if you’re ok with them. Thumbs down if you’re still not ok with them. Note: Clicker Channel 21 10/18/2010 Lecture 13 1
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Some culture: Whether “thumbs up” and “thumbs down” were the actual signals used at Roman gladiatorial combats is debated. The French “academic” painter Jean-Léon Gérôme (1872: Pollice Verso ≈ “turned thumb”) thought so and painted Vestal Virgins with “thumbs down”. This painting inspired film director Ridley Scott. But his 2000 movie Gladiator had the most powerful thumb belonging to the Emperor. Nowadays the meanings are thumbs up barb2right yes, good thumbs down barb2right no, bad Joaquin Phoenix as Commodus
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x -y z Too many missed this last time:
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Too many missed this last time:
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Chapter 26 – AC Electricity AC Voltage Sources AC Resistor circuits AC currents in a resistor AC power and RMS voltage and current AC Capacitor circuits AC voltage and current in a capacitor Reactance of a capacitor • Inductors AC voltage and current in an inductor Self Inductance and Reactance • Transformers Electrical Power in your home and Electrical safety AC circuits with R , C , and L –E RLC circuits 10/18/2010 Lecture 13 5
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AC Voltage Sources An AC Generator: A wire loop is rotated by an external force (water or hot gas turbine) in an magnetic field: The Lorentz force on the mobile charges in the moving wire creates an induced current I ind : Faraday’s induction law: The voltage is picked up by sliding contacts at the two ends of the wire loop … Real Generator: many windings • multiple magnet poles 10/18/2010 Lecture 13 6 v B θ F L side view g3404 g3398 g1856Φ g3003 g1856g1872 g1832 g3013 g3404 g1869g1874g1828sing2016
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Lecture 13 7 AC Generator: Changing Angle between Area Area Area and B Consider a static and uniform B -field to the right. A wire loop ( N windings, area A ) rotates around an axis perpendicular to B (perpendicular to the paper), with constant angular velocity ω : Only the relative orientation of B and A varies with time… The change in flux: – induced emf varies (co)sinusoidally in time, peak amplitude E 0 = ω NBA Example: a large AC generator : f = 60 Hz = ω /2 π , N= 500 , A= 3.0 m 2 , B= 0.10 T barb4right E 0 = 2 π f NBA = 120 π× 500 × 3.0 × 0.10 = 57 kV , i.e., good for High Voltage power line distribution A ω x θ B,A = ω t ( ) B d d dt dt Φ = B A 10/18/2010 B cos( ) d A B d t t ω = sin( ) A t B ω ω = - B d N dt Φ = - E sin( ) NBA t ω ω = cos d A B d t θ = AB 0 sin( ) t
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