Series and Parallel Circuits — AQA GCSE Physics
Components can be connected in series (one loop) or parallel (separate branches), which affects current, potential difference and resistance.
Series circuits
In a series circuit, components are connected in one loop:
- The current is the same through every component.
- The total potential difference of the supply is shared between the components.
- The total resistance is the sum of the individual resistances: $$R_{total} = R_1 + R_2 + R_3 \dots$$
Parallel circuits
In a parallel circuit, components are on separate branches:
- The potential difference is the same across each branch.
- The total current is shared between the branches (it splits and rejoins).
- The total resistance is less than the smallest individual resistance — adding a resistor in parallel provides another path for the current, reducing the overall resistance.
Why add resistors in parallel reduces resistance
More parallel paths means it is easier for current to flow overall, so the total resistance decreases.
Exam tips
- Series: current the same; p.d. shared; resistances add.
- Parallel: p.d. the same; current shared; total resistance is less than the smallest resistor.
- Adding a component in series increases total resistance; in parallel it decreases it.
- Be able to calculate total resistance in series.