electromagnetic induction
DESCRIPTION
Electromagnetic Induction. Michael Faraday and Joseph Henry discovered that a magnetic field could cause an electric current to flow in a conductor moving in the field. The magnetic field exerts a force on the electrons in the wire, causing them to move. - PowerPoint PPT PresentationTRANSCRIPT
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• Michael Faraday and Joseph Henry discovered that a magnetic field could cause an electric current to flow in a conductor moving in the field
• The magnetic field exerts a force on the electrons in the wire, causing them to move
• This is called the GENERATOR EFFECT or ELECTROMAGNETIC INDUCTION
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3 ways to induce a current:
Method 1: move the conductor in a magnetic field
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One end is positive and the other end is negative – a voltage is induced in the rod,
Use the third left hand rule: fingers in direction of magnetic field, thumb points in direction of WIRE MOTION, palm indicates the directions the electrons are forced
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A current will flow in the conductor if a complete electrical circuit exists
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For a moving conductor, the induced voltage is found by
V=LvB
where V = induced voltage L=length of conductor in the magnetic field in mv = speed in m/s B= magnetic field strength at right angles to the conductor
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Method 2:A moving magnet will cause an induced voltage in a conductor placed in the field of the magnet
Magnet in coil
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Method 3: a changing magnetic field can cause an induced voltage in a conductor
insulated wire(primary coil)
insulated wire(secondary coil)
Faraday's Experimnt
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Iron Core
Metal Detector Animation and Explanation
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• When the switch is closed, the current causes a magnetic field around the primary coil which increases as the current rises from zero to the maximum value
• The iron core concentrates the field lines so the secondary coil is in the magnetic field of the primary coil.
• The changing magnetic field around the primary causes a changing magnetic field around the secondary coil
• The changing secondary magnetic field will cause a voltage to be induced in the secondary coil
• The direction of current flow in the secondary will be in the opposite direction of current flow in the primary
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•Once the primary current reaches its maximum, the magnetic field is no longer changing and no voltage is induced in the secondary
• When the switch is opened (current is turned off) the magnetic field around the primary begins to reduce and induces a voltage in the secondary coil again
• The magnitude of the induced potential difference depends on the:
☺ strength of the primary magnetic fields☺ how quickly the magnetic field is changing
• Faraday’s Law of Induction:☺An induced voltage is produced by a changing magnetic field.☺The induced potential difference depends on the rate of change of the magnetic flux through the coil.
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Reading Magnetic Tape:
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Writing to a Magnetic Tape:
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Read pages 694 to 698; 738 to 740