Zhang20-2 - Electric generator Converts mechanical energy to electrical energy Consists of wire loops rotated by some external means Hydropower(e.g

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2/14/2010 1 Electric generator Converts mechanical energy to electrical energy Consists of wire loops rotated by some external means Hydropower (e.g. water falls) - Coal, oil, gas - Nuclear power The fuel is used to rotate the loops, the rest is taken care of by Faraday’s Law As the loop rotates, the magnetic flux through it changes with time This induces an emf and a current in the circuit (if the circuit is closed) The ends of the loop are connected to slip rings that rotate with the loop Connections to the external circuit are made by stationary brushes in contact with the slip rings Because the normal direction of the loop changes with time, the induce emf also changes with time even the sign changes AC (Alternating Current)
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2/14/2010 2 A loop with an area A rotates in a uniform magnetic field Magnetic flux passing through the loop changes with time: An emf will be induced ) cos( : flux Magnetic BA B Red arrow : normal direction of the plane B ) cos( t BA B t : Angle t  It can be shown that Red arrow : normal direction of the plane B ) sin( t BA t  ) sin( )] [cos( )] [cos( lim : FYI 0 t dt t d t t t ) cos( t BA B t  Calculus!
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2/14/2010 3 For N-turn loop: How to achieve greater emf - Stronger magnetic field: B - Larger loop: A - Faster rotation: - More turns (loops): N ) sin( t BA BA t t BA t BA B max max ) sin( ) sin( ) cos( NBA t max max ) sin( ? max
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This note was uploaded on 03/15/2010 for the course PHY 102 taught by Professor Luo during the Spring '08 term at SUNY Buffalo.

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Zhang20-2 - Electric generator Converts mechanical energy to electrical energy Consists of wire loops rotated by some external means Hydropower(e.g

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