Chapter 27 lecture

# Chapter 27 lecture - Exam watch ? Chapter 27 Magnetic...

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Chapter 27 Magnetic Fields and Forces November 1 at 6:30 pm Chapters 24.5-27 Watch for a practice exam next week Exam watch ?

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Magnetism Forces between objects without any net electrical charge…. . Evidence for 2 magnetic “charges”, “N” and “S” Like E field we suspect magnets create a magnetic field, B, in space around it…. .vector field Can we write Is there a “Coulomb’s Law “ for magnetism? ? B q F M M = Kinda, maybe, sorta, sure….but there are some glaring differences between B and E fields: Magnetic monopoles have never been isolated B field lines never end--they are loops!
B field lines (compare with E field lines) 1. is tangent to line at any point 3. and 5. B field lines are loops…(this is definitely not like E field lines……next slide) B A d B flux thus and dA dN B surf B = Φ = , Same Same Same

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Question 1 What is the implication of B field lines being continuous loops? Φ B is not defined for a closed (Gaussian surface) Φ B is not defined for an open surface Φ B for a closed surface will always be zero Φ B for an open surface will always be zero B Lines must begin on N magnetic charges and end on S

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Gauss’s Law for Magnetism 0 surf closed = A d B 0 = B Flux in = Flux out No magnetic monopoles Maxwell’s 2 nd equation! (differential form?) 0 = = vol surf dV B A d B
Oersted’s Experiment/Demo (1820) (connects magnetism with electricity) A current carrying wire (moving electrical charges) exerts (magnetic) forces on magnets…. . see demo Moving charges must generate B fields! (chapter 28) Newton’s 3 rd law (action-reaction) Magnets/ B fields exert magnetic forces of moving electrical charges and currents (this is chapter 27)

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Hans Christian Ørsted Danish (1777-1851) Discovery of electromagnetism While preparing for an evening lecture in April 1820 , Ørsted developed an experiment
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## This note was uploaded on 04/02/2008 for the course PHYSICS 260 taught by Professor Evrard during the Fall '07 term at University of Michigan.

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Chapter 27 lecture - Exam watch ? Chapter 27 Magnetic...

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