The force on a charged particle in a magnetic field
An electric field E exerts a force on a charge q. A magnetic field B will also exert a
force on a charge q, but only if the charge is moving (and not moving in a direction
parallel to the field). The direction of the force exerted by a magnetic field on a
moving charge is perpendicular to the field, and perpendicular to the velocity (i.e.,
perpendicular to the direction the charge is moving).
The equation that gives the force on a charge moving at a velocity v in a magnetic
field B is:
This is a vector equation : F is a vector, v is a vector, and B is a vector. The only thing
that is not a vector is q.
Note that when v and B are parallel (or at 180°) to each other, the force is zero. The
maximum force, F = qvB, occurs when v and B are perpendicular to each other.
The direction of the force, which is perpendicular to both v and B, can be found using
your right hand, applying something known as the righthand rule. One way to do the
righthand rule is to do this: point all four fingers on your right hand in the direction
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 Fall '10
 DavidJudd
 Physics, Charge, Circular Motion, Force, Magnetic Field, Electric charge, 180°

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