Electricity
Lesson overview
This lesson introduces the core physics idea, the useful equipment and the calculation or data skills used on this page.
What you will learn
Circuit comparison prompts
Use the lamp and resistor circuits to practise deciding whether current or potential difference is shared, split or the same.
Series and parallel circuits infographic
Clear explanation
In a series circuit there is only one loop, so the current is the same everywhere. Potential difference from the supply is shared between components.
In a parallel circuit there is more than one branch. Potential difference is the same across each branch, but current can split between branches.
Adding resistors in series increases total resistance because charge has more opposition around the single loop.
Key diagram
Worked examples
Series resistance
A 3 ohm resistor and a 5 ohm resistor are connected in series.
total resistance = 3 + 5
total resistance = 8 ohms
Quick checks
Choose an answer, then check your thinking.
1. What is true about current in a simple series circuit?
2. What is true about potential difference across parallel branches?
Practice questions
Question 1
Two resistors of 4 ohms and 7 ohms are in series. Calculate total resistance.
Reveal answer and marking guidance
Answer: 11 ohms.
Marking: Credit adding series resistances: 4 + 7 = 11 ohms.
Question 2
A 9 V supply has two series lamps with 4 V across one lamp. What is across the other lamp?
Reveal answer and marking guidance
Answer: 5 V.
Marking: Credit shared potential difference adding to 9 V.
Question 3
A parallel circuit has 2 A in one branch and 3 A in another. What is the current from the supply?
Reveal answer and marking guidance
Answer: 5 A.
Marking: Credit branch currents adding at the junction.
Question 4
Why do lamps in parallel usually stay bright when another branch is added?
Reveal answer and marking guidance
Answer: Each branch still gets the full supply potential difference.
Marking: Credit same potential difference across branches.
Practice ladder
Answers and marking guidance
The exact practice answers are hidden under each question so you can try first. For this lesson, marks come from using the correct physics model, choosing the right equation where needed, keeping units with values, and explaining changes with precise words such as transfer, resultant force, acceleration, evidence and uncertainty.
Common mistakes
- Saying current is shared in series.
- Adding parallel branch potential differences like a series loop.
- Forgetting current splits and recombines at junctions.
- Thinking extra series resistors make current larger.
Extension challenge
Draw one series and one parallel circuit with two lamps, then annotate current and potential difference rules.
Reveal answer
Example answer: A strong extension response names the physics model, uses accurate units and explains why the evidence supports the conclusion.
Exam-board guidance
Short board notes only. Learn the core physics above first.
AQA GCSE Physics
AQA GCSE Physics: often rewards clear physics explanations, correct equations, units and practical evidence for series and parallel circuit behaviour.
OCR GCSE Physics
OCR GCSE Physics: often values precise definitions, clear working, graph interpretation and links between models and evidence.
Pearson Edexcel GCSE Physics
Pearson Edexcel GCSE Physics: often combines the concept with equation use, data handling and practical interpretation.
Eduqas GCSE Physics
Eduqas GCSE Physics: learn the core explanation and practise applying it to unfamiliar contexts, data and practical questions.
WJEC Wales
WJEC Wales: often expects accurate terms, units and evidence-based explanations using the shared physics idea.
CCEA GCSE Physics
CCEA GCSE Physics: connect the idea to your current unit and use the same practical method language your class uses.
Next lesson
Next, continue with Specific Heat Capacity and Latent Heat.