Four identical metal cans were each filled with 200 cm3 of water at 80 ∘C80\ ^\circ\text{C}80 ∘C. Each can had a different outer surface. The cans were left to cool in the same room. The table shows the temperature of the water in each can after 20 minutes.
Table: The temperature of the water in four cans with different outer surfaces, at the start and after 20 minutes of cooling in the same room
| Can | Outer surface | Temperature at the start in ∘C^\circ\text{C}∘C | Temperature after 20 minutes in ∘C^\circ\text{C}∘C |
|---|---|---|---|
| A | matt black | 80 | 46 |
| B | shiny black | 80 | 52 |
| C | matt white | 80 | 50 |
| D | shiny silver | 80 | 61 |
Calculate the decrease in the temperature of the water in can D.
The student concluded that a matt surface is a better emitter of infrared radiation than a shiny surface. Explain how the results support this conclusion.
Give one variable, other than the volume of water and the starting temperature, that the student had to control.
The student repeated the whole investigation twice more. Explain why.
40 exam-style questions on AQA GCSE Physics 6.3 Black body radiation, covering 6.3.1 Emission and absorption of infrared radiation and 6.3.2 Perfect black bodies and radiation. Each one has a worked solution and a mark scheme showing where the marks go.