Lecture_15

Lecture_15 - The Drude Model eEt Average `drift speed v =...

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The Drude Model eE Δ t Δ t - average time between Average ‘drift’ speed: v = m e collisions For constant temperature v ~ E t m e u uE v e Δ = = , u – mobility of an electron Electron current: v nA i = i = nAuE

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E and Drift Speed In steady state current is the same everywhere in a series circuit. i i What is the drift speed? v nA i = thick thick thin thin v nA v nA = thick thin thick thin v A A v = E thick E thin Note : density of electrons n cannot change What is E ? v = uE uE thin = A thick uE thick A thin thick thin thick thin E A A E =
Question 2 mm 1 mm 1.5 . n 1 = n 2 2 . u 1 = u 2 10 18 Every second 10 18 electrons enter the thick wire. How many electrons exit from the thin wire every second? A) 10 18 C) 2 x 10 18 B) 1.5 x 10 18 D) 4 x 10 18 E) 12 x 10 18

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Direction of Electric Field in a Wire Does current fill the wire? Is E uniform across the wire? E must be parallel to the wire E is the same along the wire B C D A Δ V ABCDA = E 1 dl E 3 dl E 2 dl E 3 dl = 0 A B C D
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