Magnetic flux is defined as the number of magnetic lines of force passing normally through a surface. It is denoted by symbol Φ (phi). The S.I. unit of magnetic flux is weber (Wb). It is a scalar quantity. The CGS unit of magnetic flux is maxwell. Consider a surface having area, A in the magnetic field having magnetic flux density, 
as shown in figure 1.
Mathematically, Magnetic flux is defined as the scalar product between the magnetic flux density (
) and the vector of the surface area (
).
where,
= magnetic flux
B = magnetic flux density magnitude
A = area of surface
θ = angle between
and
Note: The direction of the vector
is always normal to the surface.
Case-1: When θ = 0°
In this case, the flux is maximum.
Case-2: When θ = 90°
In this case, the flux is minimum.
Note: Magnetic flux is usually measured with a fluxmeter.
