Lecture 19 preview mar18

Lecture 19 preview mar18 - Lecture 19 Maxwell's Equations...

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Lecture 19 Maxwell’s Equations Faraday says, “changing magnetic flux can generate electric currents” •Changing B: magnet and wire loop •Changing area: AC generator
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Induced E fields and Maxwell’s 3 rd - = Φ - = * * ) ' ( 3 ' surf path rd A d B dt d dt d l d E Law s Faraday s Maxwell X B increasing X X X Changing B fields induce E fields (that produce ξ) 2 nd Important point: take away the wire and the E fields are still there! Question 1: How does E depend on r? (r>R) A. ~r B. ~r 2 C. ~1/r D. ~1/r 2 r R dt d r E so dt d r E Φ = Φ = π 2 1 2 How about E for r<R??? Electric fields can be generated by changing magnetic flux
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(A week ago) Applications of Ampere’s Law 1. ∞ straight wire: (obvious) (cylindrical symmetry) B2πr = μ 0 I 1. B inside ∞ straight wire of radius R: (cylindrical symmetry) Ex 28.9 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I out (for r<R) ) ( 2 2 0 2 2 0 0 R r R I B R r I i r B l d B inside π μ = = = =
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Eddy Currents (getting E-motional about a backwater effect…. .) Let’s consider the motional EMF of a conducting sheet moving/spinning through a B field. Mobile charges are spun through B with v to the left. This generates downward current in the yellow-shaded region. F mag on these eddy currents is to the right---a drag/braking force on the spinning wheel: Let’s see if we can detect this braking force……… DEMOS
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Maxwell’s Round-up I l d B A d B dt d l d E q A d E B exclosed = = Φ - = = 0 0 0 μ ??
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This note was uploaded on 04/04/2008 for the course PHYSICS 240 taught by Professor Davewinn during the Spring '08 term at University of Michigan.

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Lecture 19 preview mar18 - Lecture 19 Maxwell's Equations...

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