Magnetic flux $\phi$ through a plane surface is the product of the magnetic flux density normal to the surface BN and the area A of the surface.
- S.I. unit for $\phi$ is weber(Wb) or T m2
- Base Units for Wb: kg m2 s -1 C -1
$\phi = AB_{N} \, = AB \, cos \, \theta$, where
$\theta$ is the angle between the B-field and the normal to the area A.
The weber is defined as the magnetic flux through a surface if a magnetic field of flux density 1 T exists perpendicularly to an area of 1 m2.
When a coil of N turns is placed instead,
Magnetic Flux Linkage $\Phi$ is defined as the product of the number of turns N of the coil and the magnetic flux $\phi$ linking each turn.
$\Phi = N \phi \, = NAB_{N} \, = NAB \, cos \, \theta$, where
- A is area of coil
- $\theta$ is the orientation of the coil with respect to the direction of B
The magnetic flux linkage through a coil depends on:
- number of turns in the coil
- area of the coil
- external magnetic flux density
- the orientation of the coil with respect to the direction of B
