Magnetic Fields
Magnetic Force on a 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 (or screen!). ]
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. ]
We can handle all these cases with a new vector operation, the cross product,
F = q v x B
| More about the Cross Product |
In a region where the magnetic field is B = 10 - 3 T (teslas), a proton (with q = e = 1.6 x 10 - 19 C) moves with a velocity of 1.2 x 109 m/s at an angle of 30o to the magnetic field.
What is the magnetic force on the proton?
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