The expression for the magnetic force helps
us to define the unit of the magnetic field, if one
takes q, F and v, all to be unity in the force
equation F = q [ v × B] =q v B sin q ˆn ,  where q is
the angle between v and B [see  Fig 4 2 (a)] The
magnitude of magnetic field B is 1 SI unit, when
the force acting on a unit charge (1 C), moving
perpendicular to B with a speed 1m/s, is one
newton