Magnetic Flux The number of magnetic field lines, or magnetic flux, which pass through a given crosssectional area can be calculated with the formula
Φ = B_{perpendicular}A
where
 Φ is the number of flux lines, measured in webers (Wb)

B_{perpendicular} is the magnetic field strength, measured in tesla (T)

A is the crosssectional area, measured in m^{2}
This relationship defines a tesla to be a weber/m^{2}.
As shown below by two extreme cases, the number of flux lines can vary from a maximum value of Φ = BA when the area vector, A, is perpendicular to the magnetic field lines, B, to a minimum value of zero when the area vector, A, is parallel to the field lines, B.


Φ = BA (maximum value)

Φ = B(0) = 0 (minimum value)

Earlier we saw that moving electric charges in electric currents can create magnetic fields. In the early 1830's Faraday used the concept of flux lines to explain his experimental results that an emf can be induced in a coil when it is exposed to a changing magnetic flux. 