# Magnetic flux

**Electromagnetic induction** is the process of applying magnetic fields to create electric currents in metal conductors. It is used in power generators to generate electricity as well as transformers to increase or decrease voltages.

The magnetic flux ($$\phi$$) gives an indication of the intensity of a magnetic field through a surface (such as a plane or a hemisphere) that the field penetrates.

The **magnetic flux through an area** is given by: $$$\phi=BA \cos \theta$$$ $$\phi$$ is the magnetic flux, $$B$$ is the magnetic flux density, $$\cos \theta$$ gives the flux density that is normal (i.e. perpendicular) to the surface and $$A$$ is the area of the surface.

The magnetic flux can be thought of as the **total number of field lines that passes perpendicularly through a surface.**

The **SI unit** of magnetic flux is the Weber ($$\text{Wb}$$). One weber is equivalent to one tesla metre squared ($$\text{Tm}^{2}$$)

The **magnetic flux linkage through a coil** is the sum of the magnetic flux through each turn of the coil (a coil is similar to a series of metal rings linked together).

The magnetic flux linkage through a coil of $$N$$ turns is given by: $$$\Phi=N\phi=NBA$$$ $$\Phi$$ is the magnetic flux linkage and $$\phi$$ is the magnetic flux through a single turn (ring) of the coil.