Conductors, Semiconductors & Insulators (OCR AS Physics): Revision Note

Exam code: H156

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Conductors, Semiconductors & Insulators

  • The number density of charge carriersn of a material determines how well the material conducts electricity

Value of n For Different Materials Table

Semiconductor n Value Table, downloadable AS & A Level Physics revision notes

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

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Ashika

Author: Ashika

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Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.

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