Theory
When a charged particle in a gas or liquid is acted upon by a uniform electric field, it will be accelerated until it reaches a constant drift velocity according to the formula:
where
- is the drift velocity (m/s)
- is the magnitude of the applied electric field (V/m)
- is the mobility (m2/(V.s))
In other words, the electrical mobility of the particle is defined as the ratio of the drift velocity to the magnitude of the electric field:
Electrical mobility is proportional to the net charge of the particle. This was the basis for Robert Millikan's demonstration that electrical charges occur in discrete units, whose magnitude is the charge of the electron.
Electrical mobility of spherical particles much larger than the mean free path of the molecules of the medium is inversely proportional to the diameter of the particles; for spherical particles much smaller than the mean free path, the electrical mobility is inversely proportional to the square of the particle diameter.
Read more about this topic: Electrical Mobility
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