Lecure18_Kim - Lecture 18-1 Self Induction The changing current in a coil also induces an emf in itself This phenomenon is called self-induction

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Lecture 18-1 1 Self Induction The changing current in a coil also induces an emf in itself This phenomenon is called self-induction The resulting emf is termed the self-induced emf Faraday’s Law of Induction: the self-induced emf for an inductor is given by Lenz’s Law provides the direction of the self-induced emf The minus sign expresses that the induced emf always opposes any change in current V emf , L   d N B dt   d Li   dt   L di dt
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Lecture 18-2 Self-Inductance: increasing or decreasing current i As current i through coil increases, magnetic flux through itself increases. This in turn induces counter EMF in the coil itself When current i is decreasing, EMF is induced again in the coil itself in such a way as to slow the decrease. Self-induction B N L i (if flux linked)
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Lecture 18-3 Examples of Induction Switch has been open for some time: Nothing happening Switch is just closed: EMF induced in Coil 2 - + - Switch is just opened: EMF is induced again - + Switch is just closed: EMF is induced in coil + - Back emf (counter emf)
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Lecture 18-4 Mutual Inductance (1) 2 1 2 1 1 ,2 2 () ind dN di dt dt VM  For two coils, total magnetic flux through coil 2 due to the field created by coil 1: Then, 12 1 i 2 1 N M i Define mutual inductance of coil 2 with respect to coil 1 unit: henry H 2 T m V s H AA  , B ind L d Li di VL dt dt dt       From Faraday’s law of induction, the seld-induced potential difference for a inductor (or coil) is given by 1 2 1 2 1 2 i M N  
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Lecture 18-5 Mutual Inductance (2) 1 2 1 ,1 2 1 2 () ind dN di VM dt dt     Reciprocity – a fundamental symmetry 2 1 1
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This note was uploaded on 12/07/2011 for the course PHYS 241 taught by Professor Wei during the Fall '08 term at Purdue University-West Lafayette.

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Lecure18_Kim - Lecture 18-1 Self Induction The changing current in a coil also induces an emf in itself This phenomenon is called self-induction

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