Electromagnetic induction
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Electromagnetic induction is where a current is produced in a conductor through a changing magnetic flux.
[edit] Magnetic flux
Magnetic flux is the strength of the magnetic field going through an area. It is the product of the magnetic field (B), the area (A) that it is going through and the angle (a) between the line 90 degrees to the area and the magnetic field lines. Magnetic flux is represented by the symbol Φ, therefore we can say that Φ = BAcos(a) and the resulting unit will be Tm2, where T is the unit for magnetic field and m2 is the unit for area.
The changing magnetic flux generates an electromotive force (EMF). This force then pushes free electrons in a certain way, which in turn creates a current.
[edit] Faraday's Law
Michael Faraday found that an electromotive force is generated when there is a change in magnetic flux in a conductor.
His laws states that:
where,
is the electromotive force, measured in volts;
dΦ is the change in magnetic flux, measured in webers;
dt is the change in time, measured in seconds.
In the case of a solenoid:
where,
N is the number of loops in the solenoid.
[edit] Lenz's Law
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.