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Electromagnetic Induction PowerPoint PPT Presentation

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.

Electromagnetic Induction

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Presentation Transcript

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

• This is called the GENERATOR EFFECT or ELECTROMAGNETIC INDUCTION

3 ways to induce a current:

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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• A current will flow in the conductor if a complete electrical circuit exists

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 m

v = speed in m/s

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

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

Iron Core

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insulated wire

(secondary coil)

insulated wire

(primary coil)

Metal Detector Animation and Explanation

• 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