**Magnetic flux density **(B) is defined as the force acting per unit current per unit length on a wire placed at right angles to the magnetic field.

- Units of B is Tesla (T) OR $Kg \, s^{-2} \, A^{-1}$
- B is a vector quantity

$B = \frac{F}{I l}$, where

- F is the total force acting on the wire,
- $l$ is the length of the wire,
- $I$ is the current flowing through the wire.

1 Tesla is defined as the magnetic flux density of a uniform magnetic field when a wire of length 1m , carrying a current of 1A, placed perpendicular to the field, experiences a force of 1N in a direction at right angles to both the field and the current.