Series & Parallel Circuits (AQA GCSE Physics)

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Katie M

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Katie M

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Series & Parallel Circuits

  • There are two ways of joining electrical components, in series and in parallel
    • Some circuits include both series and parallel parts

  • A series circuit consists of a string of two or more components, connected end to end:

    Series circuit, IGCSE & GCSE Physics revision notes

Diagram showing two bulbs connected in series

  • A parallel circuit consists of two or more components attached along separate branches of the circuit

Parallel circuit, IGCSE & GCSE Physics revision notes

Diagram showing two bulbs connected in parallel

Series Circuits

  • In a series circuit:
    • The current is the same at all points ie. through each component
    • The total potential difference of the power supply is shared between the components
    • The total resistance of two components is the sum of the resistance of each component

Lamps connected in a series circuit

  • In the above circuit:
    • The current from the power supply is the same as the current in both lamps I = I1 = I2
    • If the battery is marked 12 V, then the potential difference would be 12 ÷ 2 = 6 V across each lamp
    • If each lamp has a resistance of R, then the total resistance in the circuit is equal to R + R = 2R

Parallel Circuits

  • In a parallel circuit:
    • The total current through the whole circuit is the sum of the currents through the separate components
    • The potential difference across each component is the same
    • The total resistance of two resistors is less than the resistance of the smallest individual resistor

Lamps connected in a parallel circuit

  • In the above circuit:
    • Because the current splits up, the sum of currents in each branch will equal the current from the power supply I = I1 + I2
    • If the battery is marked 12 V, then the potential difference would be 12 V across each lamp
    • If each lamp has a resistance of R, then the total resistance in the circuit will be less than 2R

  • Note that the current does not always split equally – often there will be more current in some branches than in others
    • The current in each branch will only be identical if the resistance of the components along each branch are identical

  • Current behaves in this way because it is the flow of electrons:
    • Electrons are physical matter – they cannot be created or destroyed
    • This means the total number of electrons (and hence current) going around a circuit must remain the same
    • When the electrons reach a junction, however, some of them will go one way and the rest will go the other

Junctions current splitting, IGCSE & GCSE Physics revision notes

Current is split at a junction into individual branches

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Katie M

Author: Katie M

Expertise: Physics

Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.