AQA GCSE Physics

Revision Notes

2.1.3 Current, Resistance & Potential Difference

Current, Resistance & Potential Difference

  • Resistance is defined as the opposition to current:
    • The higher the resistance of a circuit, the lower the current
    • This means that good conductors have a low resistance and insulators have a high resistance
  • The symbol for resistance is R
  • It is measured in Ohms (Ω)
    • Ω is the Greek capital letter ‘Omega’
    • An Ohm is defined as one volt per ampere (1 V / A)
  • The resistance of a circuit can be increased by adding resistors (or variable resistors) to it
  • Every electrical component has a resistance, even wires
    • In exam questions, the resistance of the wires and batteries are assumed to be negligible

Resistance & Current, downloadable IGCSE & GCSE Physics revision notes

High resistance means there is lower current and vice versa

  • The current I through a component depends on both the resistance R of the component and the potential difference V across the component
    • The greater the resistance R of the component, the lower the current I for a given potential difference V across the component
    • The lower the resistance R of the component, the greater the current I for a given potential difference V across the component

Calculating Current, Resistance & Potential Difference

  • The current, resistance and potential difference of a component in a circuit are calculated using the equation:

Ohm's law, downloadable AS & A Level Physics revision notes

  • This equation can be rearranged with the help of the following formula triangle:

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

Voltage, current, resistance formula triangle

Worked Example

Calculate the potential difference through a resistor of resistance 10 Ω if there is a current of 0.3 A through it.

Step 1: List the known quantities

    • Resistance, R = 10 Ω
    • Current, I = 0.3 A

Step 2: Write the equation relating resistance, potential difference and current

V = IR

Step 3: Substitute in the values

V = 0.3 × 10 = 3 V

Exam Tip

Remember that ‘voltage’ and ‘potential difference’ are the same, either wording will be accepted in your exam answers

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