Electromagnetic Induction
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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.

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Presentation Transcript

  • 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


3 ways to induce a current: field could cause an electric current to flow in a conductor moving in the field

Method 1: move the conductor in a magnetic field

  • One end is positive and the other end is negative – a voltage is induced in the rod,

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  • 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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For a moving conductor, the induced voltage is found by electrical circuit exists

V=LvB

where V = induced voltage

L=length of conductor in the magnetic field in m

v = speed in m/s

B= magnetic field strength at right angles to the conductor


Method 2: electrical circuit exists

A moving magnet will cause an induced voltage in a conductor placed in the field of the magnet

Magnet in coil


V electrical circuit exists

Method 3: a changing magnetic field can cause an induced voltage in a conductor

Iron Core

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insulated wire

(secondary coil)

insulated wire

(primary coil)

Metal Detector Animation and Explanation

Faraday's Experimnt


  • 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


  • 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.


Reading Magnetic Tape: field is no longer changing and no voltage is induced in the secondary


Writing to a Magnetic Tape: field is no longer changing and no voltage is induced in the secondary


Read pages 694 to 698; 738 to 740 field is no longer changing and no voltage is induced in the secondary


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