p240_ct17_f07 - Physics 240 Fall 2007 Lecture #17 Second...

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Physics 240 Fall 2007 Lecture #17 Dr. Dave Winn 2405 Randall Lab winn@umich.edu Second exam tonight, 8:00-9:30 Chapters 24.2-28.4
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Exam details You may bring your notecard from the last test, plus one for this test. Practice exam and solutions online Discussion instructors Eckhause : Chemistry 1800. Discussion instructors Campbell : Chem 1400 Discussion instructor Bobkov : Dennison 182. Discussion instructor Winn: Dennison 170
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How to calculate fields from currents? For E field, use field from each charge and add them up… Biot-Savart law gives field from current element Integration yields total field For E field, calculate electric flux and use Gauss’ law to relate flux to charge inside Electric flux measures how much E field goes in an out For magnetic field, it’s wrapping around that matters: circulation For B field, Ampere’s law relates ‘circulation’ to current passing through 3 0 4 r r s id B d r r r × = π μ
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Ampere’s Law Gauss’ law relates flux of E field over area to charge inside Ampere’s law relates sum of B field along a line to current inside Formally: B d L= μ 0 I inside
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I 2 What is the total sum Σ B || Δ Lfrom Ampere’s law for this system? 1: μ 0 I 2 2: 2 μ 0 I 2 3: Zero Total current inside this loop is zero, so the net B d L is zero.
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Magnetic field of wire from Ampere’s Law B dL = μ 0 I inside B*2 π r = μ 0 I B = μ 0 I / 2 π r
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This note was uploaded on 04/04/2008 for the course PHYSICS 240 taught by Professor Davewinn during the Fall '08 term at University of Michigan.

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p240_ct17_f07 - Physics 240 Fall 2007 Lecture #17 Second...

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