Electromagnetic induction

Electromagnetic induction is where a current is produced in a conductor through a changing magnetic flux.

Magnetic flux

When a coil is introduced near a magnet (usually a bar magnet), then the magnetic lines of force passing through the coil is called magnetic flux. Magnetic flux is represented by the symbol ${\Phi}$, therefore we can say that ${\Phi}$ = BAcos(a) and the resulting unit will be $Tm^2$, where T is the unit for magnetic field and $m^2$ 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.

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

His laws state that:

$\mathcal{E} = {-{d\Phi} \over dt}$

where,

$\mathcal{E}$ is the electromotive force, measured in volts;

${d\Phi}$ is the change in magnetic flux, measured in webers;

$dt$ is the change in time, measured in seconds.

In the case of a solenoid:

$\mathcal{E} = {-N{d\Phi} \over dt}$

where,

N is the number of loops in the solenoid.

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.