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Published byArthur Hodges Modified over 5 years ago

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Electromagnetic Induction Can a magnet produce electricity?

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Michael Faraday An English scientist who was first to prove that a magnet can produce current. A magnet can produce electricity! Duh! Joseph Henry

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What conditions are necessary for a magnet to produce current? Magnet must be moving or Wire must be moving Movement causes changing magnetic field Changing magnetic field induces current

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Electromagnetic Induction The phenomenon by which an emf or current induced in a conductor due to change in magnetic field.

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What factors affect the nature of emf or current produced? Direction of motion In or out Speed of motion Polarity of magnet coming in Number of turns Area of coil

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Direction of Motion The direction of the current induced opposes the change producing it

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Speed of Motion The faster the movement is, the greater is the induced emf.

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Polarity of magnet The induced current produces a magnetic field that opposes the one causing it. Use RHR

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Number of turns The more the number of turns, the greater the emf induced.

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Laws of EM induction Faraday’s Law The induced emf across the conductor is equal to the rate at which magnetic flux is cut by the conductor.

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Magnetic Flux Product of flux density (B) and the area (A), when flux is at right angles to the area. Ø= BA Unit: Weber, Wb A weber is the flux when a unit tesla of magnetic flux density is at right angles to a unit area.

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Magnetic Flux Linkage Total flux cut by all turns of the coil Ø= BAN

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So far… EMF = d Ø /dt For single coil EMF = BA/t For many coils EMF = BAN/t For a wire EMF = Blx/t Where l is length of wire and x is distance traveled. EMF = Blv Where v is the speed

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Lenz’s Law The direction of any induced current is such as to oppose the change that causes it.

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Therefore EMF = - d Ø /dt For single coil EMF = - BA/t For many coils EMF = - BAN/t For a wire EMF = - Blx/t Where l is length of wire and x is distance traveled. EMF = - Blv Where v is the speed

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Example 1 A straight wire of length 0.2 m moves at a steady speed of 3 ms -1 at right angles to a magnetic field of flux density 0.1 T. What will be the emf induced across the ends of the wire?

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Example 2 A coil of wire having 2500 turns and of area 1 cm 2 is placed between the poles of a magnet so that the magnetic flux passes perpendicularly through the coil. The flux density of the field is 0.5 T. The coil is pulled rapidly out of the field in a time of 0.1 s. What average emf is induced across the ends of the coil?

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Investigating Lenz’s Law

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Uses of EM Induction (Generator)

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Transformer

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Uses of EM Induction

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