AQA GCSE Physics

Revision Notes

2.2.3 Comparing Series & Parallel Circuits

Comparing Series & Parallel Circuits

Current in Series & Parallel

  • In a series circuit, the current is the same at all points
  • In a parallel circuit, the current splits at junctions – some of it going one way and the rest going the other

current-series-parallel, IGCSE & GCSE Physics revision notes

Diagram showing the behaviour of current in series and parallel circuits

Potential Difference in Series & Parallel

  • In a series circuit, the voltage of the power supply is shared between the components
  • In a parallel circuit, the voltage across each component is the same

voltage-series-parallel, IGCSE & GCSE Physics revision notes

Diagram showing the behaviour of voltage in series and parallel circuits

Resistors in Series & Parallel

  • In a series circuit, the total resistance is the sum of the resistance in each component
    • Two resistors in series will have a larger overall resistance than just one
    • This is because the charge has to push through multiple components when flowing around the circuit
    • The more components the charge has to travel through, the higher the number of collisions that occur
  • In a parallel circuit, the total resistance decreases and is less than the resistance of any of the individual components
    • Two resistors in parallel will have a smaller overall resistance than just one
    • This is because the charge has more than one pathway to take, so only some charge will flow along each path
    • The more pathways there are, the smaller the amount of charge in each path

Series and Parallel Circuit Summary Table

Series Parallel Circuits Summary Table, downloadable IGCSE & GCSE Physics revision notes

Worked Example

A circuit was set up as shown in the diagram.

Comparing Series Parallel Worked Example, downloadable IGCSE & GCSE Physics revision notes

Calculate the resistance of the bulb.

Step 1: Determine the voltage across the bulb

    • The components share the potential difference of the power supply, so:

12 V – 8 V = 4 V

Step 2: Write down the equation for voltage, current and resistance

V = IR

Step 3: Calculate the current through the resistor

I = V / R = 8 / 6 = 1.33 A

Step 4: Calculate the resistance of the bulb

    • In a series circuit, the current is the same everywhere, so:

R = V / I = 4 / 1.33 = 3.0 Ω

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