Lecture21 - 1 February 25, 2008 Physics 132-Winter 2008...

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Unformatted text preview: 1 February 25, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 1 Physics 132 Introductory Physics: Electricity and Magnetism Winter Quarter 2008 Lecture 21 February 25, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 2 Electric Currents and Magnetic Fields Electric currents feel forces due to magnetic fields. They also create magnetic fields! Field lines encircle the currents which are their source. Right hand rule: Thumb along i, fingers curl in direction of B 2 February 25, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 3 Biot-Savart Law dB = 4 id s r r 3 Integration of the Biot-Savart* law gives B field for a current distribution: * (Theyre French, so the final ts are silent.) This is an inverse-square law, just like Coulombs law. 0 is the permeability constant. 4 10 7 Tm A February 25, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 4 Magnetic Field of a Long Straight Wire d B = 4 id s r r 3 = i 4 sin( ) ds r 2 y x z y r 2 = R 2 + s 2 sin( ) = sin( ) = R R 2 + s 2 B = i 4 y R R 2 + s 2 ( ) 3 2 ds = + i 2 y R R 2 + s 2 ( ) 3 2 ds + = i 2 y 1 R 2 + s 2 ( ) 1 2 s = s = = i 2 R y B falls as 1/R for an infinite wire. 3 February 25, 2008 Physics 132-Winter 2008 Prof. Jim Beatty-Ohio State 5 Living Near Power Lines Power lines carry electric power across...
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This note was uploaded on 04/18/2008 for the course PHYS 132 taught by Professor Beatty during the Winter '08 term at Ohio State.

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Lecture21 - 1 February 25, 2008 Physics 132-Winter 2008...

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