Lec15-3

# Lec15-3 - ture 15-1 ture Sources of Magnetic Fields Moving...

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cture 15- cture 15- 1 Sources of Magnetic Fields 0 2 4 μ qv r dB π r × = r \$ r 7 0 2 N 4 10 A π μ - = × ÷ Permeability constant Moving point charge: 0 2 4 μ I dl r dB π r × = r \$ r Bits of current: I Biot-Savart Law / T m A × also The magnetic field “circulates” around the wire. http://falstad.com/vector3dm/

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cture 15- cture 15- 2 Magnetic field due to a current loop Principle of superposition: 0 2 4 Idl r B r μ π × = r \$ r Ñ At the center , \$ \$ sin ( / 2) dl r dl x dl x α × = × = = r \$ \$ \$ 0 2 0 2 4 I x I x R B R dl = = ur Ñ On axis generally, 0 0 2 2 2 4 4 I dl I dl dB r R x = = + ( 29 0 3/ 2 2 2 sin 4 x I R dB dB dl R x θ = × = + 3 0 2 2 3/ 2 2 ( ) x x I R B dB R R x = = × + Ñ
cture 15- cture 15- 3 Magnetic Field At Center of Circular Arc Current 0 0 2 2 sin90 4 4 ids ids dB R R μ π = = o 0 0 2 2 2 2 ds i R R i B R φ × = × = I runs clockwise in the closed loop wires below: What is B at center?

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cture 15- cture 15- 4 Circular Loop Current as a Magnetic Dipole ( 29 3 2 2 3/ 3 0 2 2 1 x I R B R R B x x μ = × = μ + if |x|>>R 0 3 2 4 x B x π In fact, 3 0 1 2 4 x p E x πε On electric dipole axis
cture 15- cture 15- 5 READING QUIZ 1 Which of the following statements about static magnetic fields is correct ? A| Magnetic fields lines end and begin in magnetic charges called monopoles. B|

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## This note was uploaded on 12/07/2011 for the course PHYS 241 taught by Professor Wei during the Fall '08 term at Purdue.

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Lec15-3 - ture 15-1 ture Sources of Magnetic Fields Moving...

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