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# lec12 - The induced EMF will produce a current that always...

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Electromagnetic Induction In 1820, Oersted discovered that “electric current produces magnetic field”. In 1830, M. Faraday formulated a law that embodies the opposite effect: “ changing magnetic flux produces electric current” Magnetic flux is defined as – It is proportional to the number of magnetic field lines pass through the surface of the coil – The unit of Φ is Weber ( T-m 2 ) Faraday’s Law of Electromagnetic Induction – The induced EMF in a coil is equal to the rate of change of the magnetic flux through it: t N ∆Φ = ε φ Coil (of area A ) viewed edge-on B r cos BA = Φ ( N is number of turns in coil )

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Direction of Induced EMF The direction of the induced EMF is stated by Lenz’s Law: “
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Unformatted text preview: The induced EMF will produce a current that always acts to oppose the change that caused it .” Thumb points in the direction of induced current Flux increasing Fingers point down to oppose the increase B r Induced EMF RH B r Induced EMF Flux decreasing Fingers point up to oppose the decrease RH Examples Illustration Lenz’s Law – Example: A magnet moving toward a coil – Example: A copper ring moving through a magnetic field Magnetic flux through the loop increases (to the right) Induced magnetic field points to the left (to oppose the change) Induced current (Counter-clockwise) Induced current (Clockwise) No current No current No current...
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lec12 - The induced EMF will produce a current that always...

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