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Assuming a charged particle or an electron moving in a plane perpendicular to a magnetic field, they will move in a circular orbit with the magnetic force playing the role of centripetal force. The direction of the centripetal force obeys the righthand rule.
The centripetal and the magnetic forces can be given by,
F = mv^{2}/R = q v B  [4295a]
The radius of the circular path R can be given by,
R = m v/q B  [4295b]
where,
m  Mass of the charged particle or electron
v  Speed of the charged particle or electron
q  Charge of the charged particle or electron
B  Magnetic flux density
Figure 4295. Schematic illustration of orbit of a charged particle (a) and an electron (b) in a magnetic field. R is the radius of the path of the charged particle and the electron in a magnetic field.
