# Magnetic flux density

The **magnetic flux density** is a physical quantity that indicates the strength of the magnetic field at a particular point in space.

The **magnitude of magnetic force** on a moving charge is dependent on the magnetic flux density at a point.

The magnetic flux density $$B$$ is formally defined as the force per unit charge acting on a particle moving with a unit velocity in a direction perpendicular to the direction of a magnetic field.

$$$B=\frac{F_{\text{magnetic}}}{qv_{\text{perpendicular}}}$$$$$q=$$charge of the particle moving with speed $$v_{\text{perpendicular}}$$ perpendicular to the magnetic field $$\vecphy{B}$$.

It is equivalent to the force per unit length acting on a straight conductor carrying a unit current placed perpendicular to the direction of a magnetic field (note that current is comprised of moving charges and is hence subject to magnetic forces).

Both **magnetic** and **electric** forces are dependent on the respective field strengths at a point.

However, the magnetic force is unique in that it acts in a direction **perpendicular to both the direction of the motion of charges as well as the magnetic field.**

Magnetic forces also only act on moving charges.

The **SI unit** of magnetic flux density is the tesla ($$\text{T}$$). One tesla ($$\text{T}$$) is equivalent to one newton per ampere per metre ($$\text{N A}^{-1}\text{m}^{-1}$$).