Force on an Electric Charge
There is no magnetic force on a stationary electric charge.
There is no magnetic force on an electric charge when it moves along the magnetic field B.
When an electric charge moves perpendicular to the magnetic field, it experiences a force of
F = q v B
That force is perpendicular to both v and B.
[ The force F is directed out of this page. ]
For a charge that moves in some other direction, the magnetic force is
F = q vperp B
That force is perpendicular to both v and B.
[ If the velocity v lies in the plane of this page, then
the force F points out of this page. ]
The magnitude of the magnetic force Fmag on charge q moving with velocity v due to magnetic field B is given by
Fmag = q v B sin
where
is the angle between the field B and the velocity v.
We can handle all these cases with a new vector operation, the cross product,
F = q v x B
(c) Doug Davis, 2003; all rights reserved
Return to Ch 20, Magnetism
