Electricity
This lesson builds electric circuit calculations for GCSE Physics.
Use the core lesson first, then match the exam-board guidance to your school route. Many pupils meet this content through Combined Science as well as Separate Physics.
What you will learn
Exam-board fit
Exact paper labels and specification-point numbering vary by board and cohort, so match this lesson to your school route before using past-paper questions.
Circuit calculation set supplied on this page
Use the lamp, resistor and battery prompts to practise choosing the correct circuit equation from the quantities given.
Clear explanation
Circuit calculations become easier when you name the quantities. Current is rate of flow of charge. Potential difference is energy transferred per coulomb of charge.
For an ohmic resistor at constant temperature, potential difference and current are directly proportional, so V = I x R.
Power in a circuit can be found using energy transferred per second, or from potential difference and current when those quantities are given.
Key diagram
Worked examples
Charge flow from current and time
A current of 0.8 A flows for 25 s.
charge flow = current x time
charge flow = 0.8 x 25
Quick checks
Choose an answer, then check your thinking.
1. Which equation links charge flow, current and time?
2. A 4 ohm resistor has 2 A through it. What is the potential difference?
Practice questions
Question 1
A current of 3 A flows for 10 s. Calculate charge flow.
Reveal answer and marking guidance
Answer: 30 C.
Marking: Credit Q = I x t and 3 x 10 = 30 C.
Question 2
A resistor has 12 V across it and 0.5 A through it. Calculate resistance.
Reveal answer and marking guidance
Answer: 24 ohms.
Marking: Credit R = V ÷ I and 12 ÷ 0.5 = 24 ohms.
Question 3
A charge of 40 C transfers 200 J of energy. Calculate potential difference.
Reveal answer and marking guidance
Answer: 5 V.
Marking: Credit V = E ÷ Q and 200 ÷ 40 = 5 V.
Question 4
A 230 V appliance has a current of 2 A. Calculate power.
Reveal answer and marking guidance
Answer: 460 W.
Marking: Credit P = V x I and 230 x 2 = 460 W.
Exam 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
- Confusing charge in coulombs with current in amps.
- Using V = I ÷ R instead of V = I x R.
- Forgetting that potential difference is energy per charge.
- Mixing up seconds and minutes in charge-flow calculations.
Exam-board guidance
All supported routes assess the core physics idea, but they may group topics, practicals and paper wording differently.
AQA GCSE Physics
AQA GCSE Physics: use this lesson for electric circuit calculations, then check whether your class is taking Separate Physics or Combined Science.
OCR GCSE Physics
OCR GCSE Physics: the core physics idea is shared, but Gateway and Twenty First Century may organise questions differently.
Pearson Edexcel GCSE Physics
Pearson Edexcel GCSE Physics: practise the concept, the equation use and the practical language because questions often connect them.
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: check whether your class is using the current GCSE Physics route or a newer science route, then use this lesson for the shared physics idea.
CCEA GCSE Physics
CCEA GCSE Physics: connect the idea to your unit and remember that practical skills are assessed directly.
Extension challenge
Write one circuit question that uses Q = I x t and one that uses E = Q x V, then solve both.
Reveal answer
Example answer: A strong extension response names the physics model, uses accurate units and explains why the evidence supports the conclusion.
Next lesson
Next, continue with Moments, Levers and Gears.