* Magnetic flux density is defined as the number of magnetic lines of force passing normally through a unit area of a substance.* It is denoted by

**B**. The S.I. unit of magnetic flux density is

**Tesla (T)**. It is a vector quantity. The CGS unit of magnetic flux density is

**gauss (G)**. Consider a surface having area,

*A*in the magnetic field having magnetic flux density,

*as shown in figure 1*.

Generally, magnetic flux is given by

where,

= magnetic fluxB = magnetic flux density magnitude

A = area of surface

θ = angle between

and**Note:** The direction of the vector

then B is given by

If Φ is the magnetic flux passing normally through a substance of area A then the magnetic flux density B is given by

since θ = 0°