Resistivity (AQA A Level Physics): Revision Note

Resistivity

• All materials have some resistance to the flow of charge

• As free electrons move through a metal wire, they collide with ions which get in their way

• As a result, they transfer some, or all, of their kinetic energy on collision, which causes electrical heating

Free electrons collide with ions which resist their flow

• Since current is the flow of charge, the ions resisting their flow causes resistance

• Resistance depends on the length of the wire, the cross-sectional area through which the current is passing and the resistivity of the material

Electrical resistance equation

• The resistivity equation shows that:

  • The longer the wire, the greater its resistance

  • The thicker the wire, the smaller its resistance

The length and width of the wire affect its resistance

• Resistivity is a property that describes the extent to which a material opposes the flow of electric current through it

• It is a property of the material, and is dependent on temperature

• Resistivity is measured in Ω m

Resistivity of some materials at room temperature

• The higher the resistivity of a material, the higher its resistance

  • This is why copper, with its relatively low resistivity at room temperature, is used for electrical wires — current flows through it very easily

  • Insulators have such a high resistivity that virtually no current will flow through them