Revision Notes

4.2.8 Resistance

What is Resistance?

  • Resistance is the opposition to current
    • For a given potential difference:
The higher the resistance, the lower the current
  • Potential difference, current and resistance are related by the following equation:

VIR equation

VIR triangle (3), IGCSE & GCSE Physics revision notes

Use the formula triangle to help you rearrange the equation

  • The unit of resistance is the ohm (Ω)


Determining Resistance

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

IV circuit, IGCSE & GCSE Physics revision notes

A circuit to determine the resistance of a component 

  • The power supply should be set to a low EMF (voltage) to avoid heating the component – 1 or 2 volts is typically enough
  • 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 following equation:

Resistance eq

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