Resistance (CIE AS Physics)

• Resistance is defined as the opposition to current
  • For a given potential difference: the higher the resistance, the lower the current
• Wires are often made from copper because copper has a low electrical resistance
• Materials with low electrical resistance are good conductors
• The resistance of a conductor is calculated using the following equation, sometimes referred to as Ohm's law:

• Where:
  • = resistance, measured in Ω
  • = potential difference, measured in V
  • = current, measured in A
• One ohm is equivalent to one volt per ampere
  • 

• The resistance in a circuit determines the amount of charge that can flow (current)
  • A higher resistance means a smaller current
  • A lower resistance means a larger current
• All electrical components, including wires, have some value of resistance

• To find the resistance of a component, we can set up a circuit like the one shown below

Determining resistance

A circuit to determine the resistance of a component

• The power supply should be set to a low voltage to avoid heating the component, typically 1-2 V
• Measurements of the potential difference and current should then be taken 
• Finally, these readings should be used to calculate resistance