AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Series and parallel circuits: For components connected in parallel:
In a parallel circuit, components are connected across the same two points, so each branch has the full supply potential difference across it.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
In a parallel circuit, components are connected across the same two points, so each branch has the full supply potential difference across it. The current from the supply splits between the branches: the current through each branch depends on that branch's resistance, and the total current is the sum of the branch currents. Because adding a branch provides another path for charge, the total resistance of the circuit is less than the resistance of any single branch. For example, with a 6 V supply and branches of 3 Ω and 6 Ω, the branch currents are 2 A and 1 A, giving a total current of 3 A and a total resistance of 6 V ÷ 3 A = 2 Ω. This is why domestic appliances are connected in parallel: each receives the full mains potential difference and can be switched independently.
What earns the marks
- State that each parallel branch has the same potential difference across it, equal to the supply potential difference.
- State that the total current from the supply is the sum of the currents in the separate branches.
- Calculate branch currents using I = V ÷ R with the common potential difference.
- Explain that adding a parallel branch decreases the total resistance because there are more paths for charge.
- Apply the parallel circuit rules to explain why domestic appliances are connected in parallel.
Common mistakes and how to put them right
Assuming current is the same in every branch.
Put it right by stating that current splits according to each branch's resistance.
Adding branch resistances to find total resistance.
Put it right by finding total current first, then using R = V ÷ I.
Thinking total resistance rises when a branch is added.
Put it right by explaining that an extra path increases total current, so total resistance falls.
Exam tips
- Label the potential difference across each branch before calculating branch currents.
- Find the total current by adding branch currents, then use R = V ÷ I for total resistance.
- Use the phrase 'same potential difference across each branch' when explaining parallel connections.
Try the lesson
The start of the Series and parallel circuits: For components connected in parallel: lesson, made from checked teaching notes for this specification point.
Have a go first
Two lamps are connected in parallel to a battery. What is the potential difference across each lamp compared with the potential difference of the battery?
Key words
Say what each word means before you turn the card.
Potential difference in parallel branches
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Current conservation at junctions
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Total resistance and multiple paths
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Practical circuit applications
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See every definition
- Potential difference in parallel branches
- Each branch has the same potential difference across it, equal to the supply potential difference.
- Current conservation at junctions
- The total current from the supply is the sum of the currents in the separate branches.
- Total resistance and multiple paths
- Adding a parallel branch decreases the total resistance because there are more paths for charge.
- Practical circuit applications
- Domestic appliances are connected in parallel so each receives the full mains potential difference and can be switched independently.
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