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241-28_Lec-14

241-28_Lec-14 - Physics 241 Lecture 14 Y E Kim October 7...

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Physics 241 Lecture 14 Y. E. Kim October 7, 2010 Chapter 27 Section 7 Chapter 28, Sections 1 and 2 October 7, 2010 University Physics, Chapter 26 and 27 1

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October 7, 2010 University Physics, Chapter 27 2 The Hall Effect (1) Consider a conductor carrying a current i perpendicular to a magnetic field B as illustrated below makes the electrons move toward one edge of the conductor This creates and produces The Hall potential is V H = Ed where d is the width of the conductor When equilibrium is reached ( ) e i v anti parallel E , B F qv B q e   B F E B F F   E F E B F F eE vBe H H V E B V Ed v dv
October 7, 2010 University Physics, Chapter 27 3 The Hall effect can be used to measure magnetic fields by applying a known current in the conductor and measuring the resulting electric field across the conductor Earlier we had found that the drift speed of an electron in a conductor can be related to the current density J in the strip where A = dh where h is the thickness of the conductor, and n is the number of electrons per unit volume in the conductor The manetic field is given by in terms of V H , h, and n The Hall Effect (2) E B F F eE vBe i J nev A H H V E B V Ed v dv i i v Ane dhne H H H V V dhne V hne B dv di i

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Magnetic Fields from Moving Charge (1) Biot-Savart Law 0 2 4 μ qv r dB π r 7 0 2 N 4 10 A Permeability constant Moving point charge: 0 2 4 μ i ds r dB π r Bits of current: I Biot-Savart Law / T m A also The magnetic field “circulates” around the wire. ids