The direction of magnetic field lines at any point can be given by the magnetic needle. Actually, the direction of magnetic field and magnetic field lines are not in same direction. So, magnetic lines of force are rather called magnetic field line.
Similar to the electric field we can also define the magnetic flux in magnetic field.
The magnetic flux at any area can be defined as magnetic field lines crossing per unit area. It is denoted by:
Again magnetic flux passing through any small elementary area is:
Total flux passing through is:
If magnetic field is uniformly distributed then,
The unit of B is Tesla (T) and area is m2. The unit of Φ is Tm2. it is also called Wber, which is named after German physicist Willium Wber.