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Published byClare Owens Modified over 9 years ago
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Magnetic Induction Transforming energy with magnetism
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Lorentz Force Reminder F = qv B Source: Griffith, The Physics of Everyday Phenomena F is directed out of the screen.
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CPS Question B I What is the direction of the Lorentz force on the charges moving in this wire? A. B. C. D. E. F.
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– Moving Creates a Potential v B induced potential +
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Motional emf Moving a conductor through a magnetic field causes separation of charges. Back-emf (motional emf) in conductor cancels potential from motion = l vB when l, v, B all orthogonal
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Rotating Loop Creates Circuit B V V
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B V V
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Group Work a.At which position(s) does the most magnetic flux pass through the loop? b.At which position(s) does the magnetic flux through the loop change the fastest? abcde
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Group Work c.What is the current direction at these points? abcde
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Faraday’s Law Greatest flux when perpendicular Fastest change in flux / t when parallel abcde
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Rotation Powers a Generator v v Motion V V induces a potential which generates a current that charges the battery B through the field
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Lenz’s Law Explains Generator B changing field opposing field needed I
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Current in a Field Feels a Force F B I
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Loop in a Field Has Torque B I I
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Torque Turns a Motor I I current I force F B
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Group Work If the magnetic field intensifies, in what direction will the induced current be? B Which direction is the flux change? What current would oppose it? What is the Lorentz force on each side?
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How a Microphone Works microphone geophone Flux inside loop becomes more
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How a Loudspeaker Works loudspeaker induced motion of magnet current current- generated field attracts or repels magnet
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Back Potential As the motor turns, back-potential B / t opposes Faster rotation more back potential I B
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