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Electromagnetic Induction
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Motional Electromagnetic Induction
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Use a magnetic field to create a current
• emf (electromotive force) ~ potential difference
• Where does the energy come from? → work !
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Electromagnetic Induction
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Induction: a coil and a magnet
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The amount of induced emf depends on
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Strength of the magnetic field
Relative speed of the coil and magnet
Area of the loops
Number of loops
More work is required to move the magnet through a
coil with many loops.
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• Why?
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Electromagnetic Induction
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Electric guitars
The string oscillates above a permanent magnet and
coil
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Electromagnetic Induction
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Magnetic flux
The amount of a magnetic field that passes through a
surface: ΦB = BA cosθ
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Electromagnetic Induction
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Faraday’s Law
The emf is proportional to the number of loops times
the rate of change of the magnetic field in the loops
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Electromagnetic Induction
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Generators
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Mechanical energy input with electrical energy output
• Opposite of electric motors
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Electromagnetic Induction
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Transformers
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Used to increase or decrease an alternating voltage
Primary and secondary windings
• Step-up or step-down
• The iron core transfers the magnetic field from one coil to
the other
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Electromagnetic Induction
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Transformers
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Electromagnetic Induction
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Transformers
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Power pole
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