p240_ct15_f07 - Physics 240 Fall 2007 Lecture #15 Second...

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Physics 240 Fall 2007 Lecture #15 Dr. Dave Winn 2405 Randall Lab winn@umich.edu Second exam next Thursday, November 1, 8:00-9:30 Chapters 24.3-27.9 or 28.4
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Exam Coverage Do you want exam 2 to cover the first part of chapter 28 (next Tuesday’s lecture)? A) Yes B) No C) Don’t care Remember, it will be on midterm 3 along with some more difficult material if we don’t cover it now.
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Another note about magnetic force Since the magnetic force is always perpendicular to the direction of motion of a charged particle, it can do no work on it! It only changes the direction of its velocity, not its magnitude Depends on q, B, and v Quantified as: Acts in a direction perpendicular to both v and B ( ) θ sin qvB B v q F = × = r r r
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Charge moving in constant B field Assume v B F = qvB in direction to both v and B Causes circular motion! mv 2 /r = qvB r = mv / qB This is called the magnetic gyroradius
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How long to go around… How long does it take for a charged particle in circular motion to orbit once? Independent of v, depends only on q/m ratio Consider some particles which all have the same q/m (like electrons) Fast particles move in large circles, slow move in small circles, but each takes the same amount of time to cycle! qB m qB mv v v r π ππ 2 2 2 = Τ = = Τ
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What if v is not to B? Imagine v has components
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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_ct15_f07 - Physics 240 Fall 2007 Lecture #15 Second...

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