Electron Drift Velocity

Electron Drift Velocity

In the specification it says that you need to know how to:

1. State what is meant by the term mean drift velocity of charge carriers.
2. Select and use the equation I = nAve
3. Describe the difference between conductors, semiconductors and insulators in terms of number density (which is n in the equation)

Random picture to take up space

The mean drift velocity is the average displacement travelled by the electrons along the wire per second.

That sentence is summarised by the equation:

v = (I/e)/nA

or

I = nAve

where:

I = Current, (amps, A)

n = Number density, (m-3)

A = Cross-sectional area, (m2)

v = Drift velocity (ms-1)

e = Electronic charge, which is 1.6 * 10-19 (coulombs, C)

You need to know how to rearrange the formula depending on what information is given to you in questions and you might have to use other formulas to get missing information to work out the answer. For example, if you don't know the current, in a question, you can use I = Q/t to work it out.

Drift velocity in other materials

Different types of material have a different number density. This is summarised below.

Conductor (e.g Copper)             = Large number density

Semiconductor (e.g Silicone)    = Small number density

Electrolyte (e.g Brine)               = Altered by doping (not always the same)

Insulator (e.g Wood)                 = Irrelevant

That's it.

(by Arjun)