8.4: mean drift velocity

Graphene’s unusual composition gives it a huge number of free electrons. The number of free charge carriers per unit volume (the number density) of graphemes is even greater than that of copper, making it an outstanding electrical conductor

Which material is an outstanding electrical conductor

Number of free electrons per cubic metre of material

What is the number density

Higher the number density, the greater the number of free electrons per m^3 and so the better the electrical conductor

Higher the number density, _____ the electrical conductor

3; insulators, semiconductors and conductors

How many groups can we classify materials according to their number density and what are they

Conductors - very high number density

insulators have a much lower value

semiconductors in between the two

Differentiate between the 3 types of metals based on their number density

Conductors - of the order 10^28m^-3

Semiconductors - around 10^17

Insulators - much lower

What are the values of the 3 types of materials based in number density

Semiconductors have a much lower number density than metals, so in order to carry the same current, the electrons in semiconductors need to move much faster. This increases the temperature of the semiconductor

Explain a fact relevant in the design of computers

Silicon

What materials are processors used in computers made of

Free electrons repeatedly collide with the positive metal ions as they drift through the wire towards the positive terminal. The reason it turns on so quickly is that all the free electrons in the wire start moving almost at once

How does a filament lamp turn on so quickly

I = A n e v

Where

I is the electric current in the conductor in amperes

A is the cross-sectional area of the conductor in m^2

e is the elementary charge (1.60\*10^-19)

n is the number density

v is the mean drift velocity of the charge carriers in ms^-1

What is another equation for electric current

Greater

The narrower the wire, the _____ the drift velocity must be in order for the current to be the same