Conductors, Semiconductors & Insulators
- The number density of charge carriers, n of a material determines how well the material conducts electricity
Value of n For Different Materials Table
Conductors
- Conductors have a very large value of n
- This is often in the range of 1028 m-3
- This means there are many free electrons per unit volume moving through the material
- Since current is the rate of flow of electrons, this makes them very good electrical conductors
- Examples of good electrical conductors are copper, aluminium and calcium
- This is why electric wires are often made from copper and aluminium
Semiconductors
- Semiconductors are materials that have a conductivity between conductors and insulators
- Their conductivity depends on their temperature
- At low temperatures, their resistivity rises, therefore their conductivity falls
- At high temperatures, their resistivity falls, therefore their conductivity rises
- Metal conductors behave in the opposite way
- Examples of semiconductor materials are silicon and germanium
- They are often used to make electronic devices such as diodes and transistors
- Semiconductors have very intermediate conduction properties
- This means they are neither very good nor very poor in terms of their conducting properties
- Therefore, semiconductor materials undergo doping
- This is when impurities are added to the material
- This helps improve their conducting properties, by increasing the value of n
Insulators
- Insulators have a very small value of n
- This is close to 0
- This means there are next to no free electrons per unit volume moving through the material
- With no current, this makes them very poor electrical conductors
- Examples of electrical insulators include plastic, rubber and glass
- These are useful for making parts of an object in which heat or electricity should not to flow for safety reasons eg. the casing of a plug
