Lec21 - Lecture 21 Lecture 21-1 Transformer AC voltage can...

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Unformatted text preview: Lecture 21 Lecture 21-1 Transformer AC voltage can be stepped up or down by using a transformer . AC current in the primary coil creates a time-varying magnetic flux through the secondary coil via the iron core. This induces EMF in the secondary circuit. Ideal transformer (no losses and magnetic flux per turn is the same on primary and secondary). (With no load) 1 2 1 2 B turn d V V dt N N = = = step-up step-down 1 2 1 2 N N V V < < 1 2 1 2 N N V V > > 11 22 IV IV = conservation of energy proportional to average power Lecture 21 Lecture 21-2 Maxwells Equations (so far) Gausss law inside S Q EdA = ca ca i I Gausslaw for magnetism S BdA = ca ca i I Faradays law B C d Edl dt = caa i I Amperes law * C Bdl I = caa i I Lecture 21 Lecture 21-3 Parallel-Plate Capacitor Revisited S S Bdl I = ca a i I For surface S 1 , I s = I , but for surface S 2 , I s = 0 ?? Wait, LHS is the same (because C is the same)! You could make this work if a fictitious current I d is added to I s in such a way that I d is zero for S 1 but is equal to I for S 2 . E dQ dV AdV I C dt dt d dt dE d A dt dt...
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This note was uploaded on 04/07/2008 for the course PHYS 241 taught by Professor Wei during the Spring '08 term at Purdue University-West Lafayette.

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Lec21 - Lecture 21 Lecture 21-1 Transformer AC voltage can...

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