Free GCSE Physics lesson: Current and Resistance
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Free Lessons -> GCSE / Key Stage 4 -> Physics -> Current and Resistance

Lesson 11 · GCSE / Key Stage 4 · Physics

Current, potential difference and resistance

Use the core circuit equations linking charge, current, potential difference, energy and resistance.

Qualification: GCSE Subject: Physics Circuits

Electricity

Lesson overview

This lesson introduces the core physics idea, the useful equipment and the calculation or data skills used on this page.

FocusCircuit quantities and equations
Time45-60 minutes
EquipmentCalculator and circuit equation sheet if available.
Practical linkNo separate practical method focus
Maths tagsM1 substitution with units

What you will learn

  • Use current = charge divided by time.
  • Use potential difference = energy transferred divided by charge.
  • Use resistance = potential difference divided by current.
  • Choose the correct circuit equation from the quantities in the question.

Circuit calculation set

Use the charge, energy and resistor data to practise selecting the correct equation before substituting.

Current, potential difference and resistance infographic

Infographic explaining GCSE Physics current, potential difference and resistance, including current as charge flow, potential difference as energy per coulomb, resistance, Ohm's law and correct meter placement.
Use this visual to distinguish current, potential difference and resistance before choosing an equation.Download visual

Clear explanation

Circuit questions become easier when you identify the quantity being asked for before choosing an equation.

Current measures charge flow each second. Potential difference measures energy transferred per coulomb. Resistance compares potential difference with current.

Always keep units visible: amperes, coulombs, seconds, volts, joules and ohms tell you which equation fits.

Key diagram

Ammeter and voltmeter placement in a component circuit A circuit diagram shows an ammeter in series with a resistor and a voltmeter connected in parallel across the resistor. A resistor V ammeter in series voltmeter in parallel
Diagram: the meter positions support the difference between current through a component and potential difference across it.

Worked examples

Finding potential difference

A component transfers 48 J of energy to 8 C of charge.

potential difference = energy transferred ÷ charge

potential difference = 48 ÷ 8 = 6

Answer: The potential difference is 6 V.

Quick checks

Choose an answer, then check your thinking.

1. Which equation links charge, current and time?

2. A 4 V component has 2 A through it. What is the resistance?

Practice questions

Question 1

A current of 0.8 A flows for 30 s. Calculate charge.

Reveal answer and marking guidance

Answer: 24 C.

Marking: Credit Q = I t and 0.8 x 30 = 24 C.

Question 2

A charge of 5 C transfers 45 J. Calculate potential difference.

Reveal answer and marking guidance

Answer: 9 V.

Marking: Credit V = E ÷ Q and 45 ÷ 5 = 9 V.

Question 3

A resistor has 12 V across it and current 0.25 A. Calculate resistance.

Reveal answer and marking guidance

Answer: 48 ohms.

Marking: Credit R = V ÷ I and 12 ÷ 0.25 = 48 ohms.

Question 4

Why should you not say current is energy?

Reveal answer and marking guidance

Answer: Current is rate of charge flow; energy transferred is measured in joules.

Marking: Credit clear distinction between charge flow and energy.

Practice ladder

FluencyRecall the key definition, unit, equation or model before using the lesson questions.
ApplicationApply circuit quantities and equations to an unfamiliar device, practical setup or data description.
Practical interpretationUse evidence, graph features, uncertainty, method quality or conclusion wording where the question asks you to evaluate.
Maths skillM1 substitution with units

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

  • Mixing up charge and energy.
  • Using current = time divided by charge.
  • Forgetting that V means joules per coulomb.
  • Dropping units after calculation.

Extension challenge

Create three circuit equation triangles and write one original question for each equation.

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 circuit quantities and equations.

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 Series and Parallel Circuits.

Previous lesson: Energy ResourcesBack to GCSE Physics lessonsNext lesson: Series and Parallel Circuits