# Lec15-1 - Lecture 15-1 Calculation of Torque Suppose the coil has width b(the side we see and length a(into the screen The torque about the center

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Lecture 15-1 Calculation of Torque Suppose the coil has width b (the side we see) and length a (into the screen). The torque about the center is given by: 2 sin 2 b τ r F F F IaB      sin sin Iab B IAB  area of loop • Define magnetic dipole moment by IAn  B   where n is normal to the loop with RHR along I . E p

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Lecture 15-2 Potential Energy of Dipole Work must be done to change the orientation 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 sin Therefore,   θ θ μB U cos θ U cos B x F F . B U
Lecture 15-3 Van Allen belts

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Lecture 15-4 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 perpendicular to both the applied E and B . Determines the sign and number of carriers. Measures B . E H E H
Lecture 15-5 Carrier Sign and Density from Hall Effect Sign and density of charge carrier is determined at equilibrium     0 H d H H H d q E q v B E E d V v B Bd Bd   and   / dd HH JI n v q v qA BId BI n V qA V q A d    Hall voltage E H E H B d A nq I V H ) / ( This relation can also be used to detect an unknown field strength B.

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## This note was uploaded on 04/23/2011 for the course PHYS 241 taught by Professor Wei during the Spring '08 term at Purdue University-West Lafayette.

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Lec15-1 - Lecture 15-1 Calculation of Torque Suppose the coil has width b(the side we see and length a(into the screen The torque about the center

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