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Unformatted text preview: Chapter 29: Electromagnetic Induction, Maxwells Equations In this chapter so far in this course, have limited our attention to timein dependent fields static electric fields from charges at rest Gausss law static magnetic fields from steady currents Amperes law new source of electric field: a changing magnetic field! Faradays law new source of magnetic field: a changing electric field! Maxwells great insight Maxwells equations complete set of equations for obtaining , E B from known charges and currents Discovery of Induction (291) we know a current causes a B field, but can a B field cause a current? on August 29, 1831 in London, Michael Faraday connected a battery through a switch to a wire wrapped around one half of an iron ring, and connected a galvanometer to a w wrapped around the other half of the iron ring ire galvanometer needle deflected when current switched on or switched off, but not while steady current flowing Joseph Henry also discovered induction in Albany, NY, at nearly same time coil 1 connected to battery and variable resistor creates a variable B near coil 2 no needle deflection for steady current v6.0 RS/BQ F10 101 increasing B causes rightward deflection of needle R decreasing B causes leftward deflection 1 2 E reversing current in coil 1 reverses effect in coil 2 we see that a changing magnetic field from the first coil produces a current in the second coil magnetic induction of current bar magnet near coil connected to galvanometer N S no deflection (no current) when magnet at rest we see that moving the magnet changes the amount of B cutting through the coil changing the strength of a nearby electromagnet similarly induces a current in the coil G R but is it the magnetic field which directly causes the current? A B=0 (and constant) Will there be an induced current if the Bfield doesnt touch the wires? Y e s ! we will need the notion of magnetic flux and the concept of changing magnetic flux inducing a current. v6.0 RS/BQ F10 102 Faradays law (292) statement of Faradays law of induction : an EMF is induced around any loop by a change of magnetic flux through the loop flux through loop can be determined using any open surface S bounded b the closed loop C y v6.0 RS/BQ F10 103 the induced EMF E (in volts) around the loop equals the negative time C rate of change of the magnetic flux B through the loop current I flows in the direction of E if the loop is closed and it is made of a conducting material....
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This note was uploaded on 08/25/2011 for the course PHYSICS II 33107 taught by Professor B.quinn during the Summer '10 term at Carnegie Mellon.
 Summer '10
 B.QUINN

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