The direction of magnatic field lines at any point can be given by the magnatic needle. Actually, the direction of magnatic field and magnatic field lines are not in same direction. So, magnatic lines of force are rather called magnatic field line.
Similar to the electric field we can also define the magnatic flux in magnatic field.
The magnetic flux at any area can be defined as magnetic field lines crossing per unit area. It is denoted by
Again magnatic flux passing through any small elementary area is
total flux passing through is
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.
so the magnetic field can be defined as the magnatic flux per unit area. It is also called magnatic flux density. Its unit is Wbm‑2. So, 1T = 1 Wbm‑2