Electromagnetic induction

production of voltage by a varying magnetic field

Electromagnetic induction is where a voltage or current is produced in a conductor by a changing magnetic flux. It may happen when a magnet is moved in a solenoid, or when a solenoid is constantly moved in a stationary magnetic field, thus changing the magnetic flux.

Magnetic flux change

When a coiled wire is introduced near a magnet, the magnetic lines of force pass through the coil. This causes the magnetic flux to change. Magnetic flux is represented by the symbol  , therefore we can say that   = BAcos(a) and the resulting unit will be  , where T is the unit for magnetic field and   is the unit for area.

The changing magnetic flux generates an electromotive force (EMF). This force moves free electrons in a certain way, which constitute a current.

Faraday's law change

Michael Faraday found that an electromotive force is generated when there is a change in magnetic flux in a conductor.

His laws state that:



  is the electromotive force, measured in volts;

  is the change in magnetic flux, measured in webers;

  is the change in time, measured in seconds.

In the case of a solenoid:



N is the number of loops in the solenoid.

Lenz's law change

The negative sign in both equation above is a result of Lenz's law, named after Heinrich Lenz. His law states that the electromotive force (EMF) produces a current that opposes the motion of the changing magnetic flux.

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