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Current In Series & Parallel (AQA GCSE Combined Science: Synergy: Physical Sciences): Revision Note

Exam code: 8465

Written by: Katie M

Updated on 6 March 2026

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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

Diagram comparing current in series and parallel circuits: in the series circuit current is the same at all points; in the parallel circuit current splits at junctions and the branch currents add up to the total current — **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

Diagram comparing voltage in series and parallel circuits: in the series circuit voltage is shared between components; in the parallel circuit voltage across each component equals the supply voltage — **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

Summary table comparing series and parallel circuits: current (same everywhere in series; splits at junctions in parallel), voltage (shared in series; same across each component in parallel), resistance (total equals sum of individual values in series; total is less than the smallest individual value in parallel)

Worked Example

A circuit was set up as shown in the diagram.

Circuit diagram showing a series circuit with a 12 V battery, a 6 Ω resistor with 8 V across it, and a bulb with unknown resistance — used to calculate the resistance of the bulb

Calculate the resistance of the bulb.

Answer:

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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