Topic 5 – Light and the electromagnetic spectrum — Edexcel GCSE Physics
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Topic 5 – Light and the electromagnetic spectrum explained
This core practical asks you to plan and carry out a fair test of how surface nature changes thermal energy radiated or absorbed.
Read the full explanation
Use identical containers (for example metal cans or boiling tubes) wrapped in different surfaces: matt black, shiny silver foil, white, and a plain control. For emission, fill each with hot water at the same starting temperature, place a thermometer in each, and record temperature at fixed intervals as they cool; the fastest fall shows the greatest radiation. For absorption, fill with cold water and place under identical lamps at equal distance, recording the rise. Control starting temperature, volume, container size, distance and room conditions, and repeat to average. Plot temperature against time and compare gradients.
Your focus
- Plan a fair test that varies surface nature while controlling other variables
- Collect and tabulate temperature data at timed intervals for each surface
- Compare rates of thermal energy transfer and draw a supported conclusion
Topic 5 – Light and the electromagnetic spectrum exam tips
Marking Points
- Describes a method that varies the nature of the surface while keeping container, volume and starting temperature the same
- Records temperature at regular timed intervals for each surface and compares the rate of change
- Identifies the matt black surface as radiating and absorbing the most thermal energy and the shiny surface the least
- Explains that a control variable such as distance from the lamp or room temperature is held constant to make the test fair
- Plots temperature against time and uses the gradient to compare rates of energy transfer
Examiner Tips
- 💡State clearly which variable you change, which you measure and which you control.
- 💡Give a numerical interval, such as every 30 seconds, rather than saying 'regularly'.
- 💡Link your conclusion to the rate of temperature change, not just the final temperature.
Common Mistakes
- Changes more than one variable at once, such as using different containers and different surfaces; keep the container identical and vary only the surface
- Reads the thermometer only at the start and end; record at regular intervals so a rate can be compared
- Assumes the shiny surface absorbs most because it looks bright; recognise that shiny surfaces reflect and absorb least