3.06 Summary.
- A free electron is an electron within a material that is not attached to its parent atom. It is a mobile charge carrier.
- It is free electrons that move to produce current flow.
- If a material has a large number of free electrons, it will be a good conductor of electricity.
- If a material has very few free electrons, it will be a poor conductor of electricity ( and a good insulator).
- Number density (n), is a measure of the number of mobile charge carriers (free electrons) per cubic metre.
- Conductors have a very high number density, insulators have very low number density and semiconductors somewhere in between.
- Free electrons move with random motion due to thermal energy, (very short very fast movements with random changes of direction).
- Thermal energy does not contribute to current flow, because there is no overall displacement of electrons from one point in the material to another.
- When an e.m.f. is applied, it causes the free electrons to drift at a speed of around 1mms-1, (towards the positive terminal (true electron flow)).
- The current flowing can be calculated using I = naqv.
