• 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 cause?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?? m

Resistivity of some materials at room temperature

• The higher the resistivity of a material, the higher its resistance
  • Copper has a relatively low resistivity at room temperature, and so is used for electrical wires
  • This is because current flows through it very easily
• Insulators have such a high resistivity that virtually no current will flow through them