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Unformatted text preview: Lecture 15 Lecture 151 Potential Energy of Dipole • Work must be done to change the o rientation of a dipole (current loop) in the presence of a magnetic field. •Define a potential energy U (with zero at position of max torque) corresponding to this work. ∫ ° ≡ θ τdθ U 90 ⇒ ∫ ° = θ θdθ μB U 90 sin Therefore, [ ] θ θ μB U ° − = 90 cos ⇒ θ μB U cos − = ⇒ U μB =− a a i B x θ a F a F a μ . Lecture 15 Lecture 152 Potential Energy of Dipole Illustrated B x μ B x μ B x μ τ = 0 U =  μ B τ = 0 U = μ B negative work τ = μ B X U = 0 positive work (by YOU) min. energy max. energy max torque Lecture 15 Lecture 153 Hall Effect •A conducting strip in crossed E and B fields •Applied E along the strip leads to a charge buildup on the sides of the strip and thus an electric field E H develops ⊥ to both applied E and B . h Determines the sign and number of carriers. h Measures B . E H E H () () H d H H H d qE qv B E Ew V v B Bw Bw ± +± × = ∴ = = = ca a ca Lecture 15 Lecture 154 Sources of Magnetic Fields 2 4 μqvr dB π r × = a ɵ a 7 2 N 4 10 A...
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This note was uploaded on 04/07/2008 for the course PHYS 241 taught by Professor Wei during the Spring '08 term at Purdue University.
 Spring '08
 Wei
 Current, Energy, Potential Energy, Work

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