Lecture_13

# Lecture_13 - F1 B N I 1 x 2 By RHR-1, we see that the force...

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N S B x I 1 2 By RHR-1, we see that the force on segment 1 is up: F 1 Likewise, we see that the force on segment 2 is down: F 2 Thus, the loop rotates clockwise as viewed from above: N S B The net force on the loop is zero , since F 1 = F 2 . But, the is not zero! This leads to a rotation! τ What is the magnitude of the net torque on the loop? φ sin NIAB Net = N = the number of loops of wire I = the current A = cross-sectional area of the loop B = magnetic field = the angle between the magnetic field and the normal to the loop’s surface x Normal to the loop’s surface

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Split-ring commutator The net torque depends on the quantity NIA, which is called the magnetic moment of the loop: φ τ sin NIAB Net = , sin μ B = where NIA = is the magnetic moment. Units? [ ] [ ] 2 m A Area Current = × DC Electric Motors
21.7 Magnetic Fields Produced by Currents Moving charges experience a force in magnetic fields. Currents also feel a force in a magnetic field. Until 1820 everyone thought electricity and magnetism were completely separate entities. Then Hans Christian Oersted discovered the following: Electric currents create magnetic fields! A more general statement is that moving charges create magnetic fields. This discovery helped create the field of Electromagnetism. What do the magnetic field lines look like around a long, straight, current-carrying wire? The current produces concentric circular loops of magnetic field around the wire. Remember, the magnetic field vector at any

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## This note was uploaded on 04/24/2010 for the course PHYS 2002 taught by Professor Blackmon during the Spring '08 term at LSU.

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Lecture_13 - F1 B N I 1 x 2 By RHR-1, we see that the force...

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