GCSEScienceAQACombined Science: TrilogyPhysicsRevision NotesElectricitySeries & Parallel CircuitsComparing Series & Parallel Circuits

Comparing Series & Parallel Circuits (AQA GCSE Combined Science: Trilogy: Physics): Revision Note

Exam code: 8464

Written by: Katie M

Reviewed by: Caroline Carroll

Updated on 9 October 2026

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
The total current from the supply is the sum of the currents in the branches
With identical components and the same supply, the total current is lower in a series circuit than in a parallel circuit, because the total resistance is greater

Two circuit diagrams, each with a battery and two lamps. In the series circuit the current I is the same everywhere; in the parallel circuit the total current I1 + I2 splits at the junction into I1 and I2, one through each lamp.

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

Two circuit diagrams with voltmeters, each with a battery and two lamps. In the series circuit the voltmeters across the lamps read V1 and V2, and the voltmeters across the supply and across both lamps together read V1 + V2; in the parallel circuit there are voltmeters across the supply and across each lamp, all reading the same.

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
- For the same potential difference, more charge can flow each second, so the total current from the supply is larger
- The more pathways there are, the larger the total current and the smaller the total resistance

Series and Parallel Circuit Summary Table

Table comparing a series and a parallel circuit, each with three resistors R1, R2 and R3 and supply voltage Vin. Series: Vin = V1 + V2 + V3, Iin = I1 = I2 = I3 and Rtotal = R1 + R2 + R3. Parallel: Vin = V1 = V2 = V3, Iin = I1 + I2 + I3 and Rtotal is less than R1 + R2 + R3.

Worked Example

A circuit was set up as shown in the diagram.

Series circuit with a 12 V battery, a lamp and a 6 Ω resistor. A voltmeter connected across the resistor reads 8 V.

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

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

I would just like to say a massive thank you for putting together such a brilliant, easy to use website.I really think using this site helped me secure my top gradesin science and maths. You really did save my exams! Thank you.

Beth
IGCSE Student

This website is soooo useful and I can’t ever thank you enough for organising questions by topic like this. Furthermore, the name of the website could not have been more appropriate as it literally did SAVE MY EXAMS!

Fathima
A Level Student

Incredible! SO worth my money, the revision notes have everything I need to know and are so easy to understand. I actually enjoy revising! It makes me feel a lot more confident for my GCSEs in a few months.

Kate
GCSE Student

Absolutely brilliant, both my girls used it for A levels and GCSE. It's saves on paper copies, also beneficial exam questions ranked from easy to hard. It's removed a lot of stress from the exams.

Sameera
Parent

Just to say that your resources are the best I have seen and I have been teaching chemistry at different levels for about 40 years

Mark
Chemistry Teacher

Excellent