# ch20notes - Chapter 20 Notes College Physics by...

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Chapter 20 Notes College Physics by Giambattista et al. John B. Ross, Ph.D. IUPUI Physics Dept. How does the electric company generate electricity? Loops of wire Magnet **DEMO!! Motion Magnetic Flux Φ “A-B-C” measure of the flow of B field through a loop cos AB B SI unit: weber (Wb) θ You generate electricity whenever you change A, B, or C. Faraday’s Law of Electromagnetic Induction E = t N B  Effect is magnified by the number of turns. The faster the change in flux, the greater the emf. Induced current Magnitude I = | E |/ R Direction Lenz’s Law Lenz’s Law Procedure – to find the direction of induced current: 1) Determine whether Δ Φ B is (+) or (–). 2) For Δ Φ B (+), point your right thumb against the B field; For Δ Φ B (–), point your right thumb with the B field; 3) Curl your fingers = direction of induced current. “The induced current moves in such a way to oppose the change in magnetic flux.”

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Unformatted text preview: Power Distribution System devised by Nikola Tesla discuss feud between Edison and Westinghouse, ac vs. dc plants Chapter 20 Notes College Physics by Giambattista et al. John B. Ross, Ph.D. IUPUI Physics Dept. Advantages of AC Power: cheaper and easier to generate adapt – transformers transmit – less heat loss may be rectified – cheaply converted to dc power Transformers iron core primary coil secondary coil E 1 E 2 N 1 N 2 Primary generates an ac magnetic field causing an induced emf in the secondary. The change in flux through the primary equals that of the secondary so 1 2 1 2 N N E E (by flux conservation) I 1 E 1 = I 2 E 2 (by energy conservation)...
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