This Science video introduces teachers to a lesson in which pupils pose testable questions and carry out a comparative enquiry to investigate how the number of bulbs affects brightness in a circuit. Pupils will review what makes a question testable – considering safety, available equipment, time, and whether the question will lead to useful results.

This video is part of Kapow Primary’s Science scheme – electricity. It supports teachers in leading a comparative test where the number of bulbs is the independent variable and brightness is the dependent variable. All other variables must be kept the same. Pupils should collect discrete data and display it as a bar chart. Check that your bulbs and batteries are working ahead of time, and remind pupils that adding more bulbs makes the light dimmer because the current slows down and less energy is transferred to each bulb per second. Use the circuit model analogy – passing cups around more slowly with more people – to support understanding. Extension opportunities include using an ammeter to show how current changes as more bulbs are added.

Science, key stage 2, Year 4, Energy: Electricity and circuits, Lesson 5: Investigating bulb brightness