Lecture_15_(Chap.20) - Twice the Length Nichrome wire...

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Twice the Length Nichrome wire (resistive) V nAu nAuE i L L i i 1 2 Quantitative measurement of current with a compass L 2 Current is halved when increasing the length of the wire by a factor of 2. 1
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Two Identical Light Bulbs in Series V nAu nAuE i Identical light bulbs L Two identical light bulbs in series are the same as one light bulb with twice as long a filament: 2 1 LL ii 2 1 2 2 Measurement: Electron mobility in metals decreases as temperature increases! Conversely, electron mobility in metals increases as temperature ecreases. Thus, the current in the 2- ulb circuit is slightly dec e ses. us, e cu e e bu b c cu s s g y more than that in the one-bulb circuit. 2
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Doubling the Cross-Sectional Area Loop: emf - EL = 0 emf i nAuE nAu L Electron current in the wire increases by a factor of two if the cross- sectional area of the wire doubles. ichrome wire Nichrome wire 3
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Two Light Bulbs in Parallel L V nAu nAuE i L … length of bulb filament 1. Path ABDFA : 2 emf  E B L 0 E B 2 L 2. Path ACDFA: 2 i F 2 emf E C L 0 E C L C B E E 3. Path ABDCA: i B = i C i batt = 2 i B 0 L E L E C B C B E E We can think of the two bulbs in parallel as equivalent to increasing the cross-sectional area of one of the bulb filaments. 4
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Long and Round Bulb in Series L R A A  L L L uE nA i only round bulb: uE nA i R R R L R i i L L R R E A E A 0 2 L E emf R emf E 2 R L R L E A A E R L E E  L R 0 2 L E L E emf L R L R R R L R R L R A A LE E A A L LE L E L E emf 1 2 f f L emf A A L emf E L R R 2 1 2  The round bulb doesn’t light up!
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This note was uploaded on 04/23/2011 for the course PHYS 272h taught by Professor Staff during the Spring '08 term at Purdue University-West Lafayette.

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Lecture_15_(Chap.20) - Twice the Length Nichrome wire...

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