Resistance (CIE A Level 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. This is also known as a good conductor
• The resistance R of a conductor is defined as the ratio of the potential difference V across to the current I in it

Resistance of a component is the ratio of the potential difference and current

• Resistance is measured in Ohms (Ω)
• An Ohm is defined as one volt per ampere
• The resistance controls the size of the current in a circuit
  • A higher resistance means a smaller current
  • A lower resistance means a larger current

• All electrical components, including wires, have some value of resistance

Determining Resistance

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

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 from the voltmeter and ammeter respectively
• Finally, these readings should be substituted into the resistance equation