Magnetic flux (ɸ). The total lines of force in a magnetic field are called magnetic flux. The S.I unit of magnetic flux is weber (Wb). It is defined as the flux which, linking in a single turn coil, induces an e.m.f of one volt when the flux is reduced to zero at a uniform rate in one second.
Flux density (B). It is given by the flux passing per unit area through a plane at right angles, to the flux. It is usually designated by the capital letter B and is measured in weber/metre2 (Wb/m2). Flux density is also known as magnetic induction.
If ɸ Wb is the total flux passing normally through an area of A m2, then