A catering business is preparing an outdoor market stall.
A tray of food is kept at a temperature of 60 ∘C60\,^{\circ}\mathrm{C}60∘C.
Give the main type of electromagnetic radiation emitted by the tray.
A metal cover over the tray becomes warm and loses energy by radiation. The cover can have a shiny finish or a matt black finish.
The table gives the average power transferred from each finish by radiation when the covers are at the same temperature.
| Surface finish | Average power transferred by radiation in W\mathrm{W}W |
|---|---|
| shiny | 24 |
| matt black | 39 |
Explain which finish should be selected to reduce this energy transfer.
The business needs an awning that will remain as cool as possible in bright sunlight. It tests a white sample and a matt black sample.
The samples are otherwise identical, differing only in surface finish. They have the same area and thickness, both start at 20 ∘C20\,^{\circ}\mathrm{C}20∘C and receive the same sunlight under the same conditions for 15 minutes.
| Surface finish | Temperature after 15 minutes in ∘C^{\circ}\mathrm{C}∘C |
|---|---|
| matt black | 38 |
| white | 29 |
Explain which surface finish should be selected for the awning.
96 exam-style questions on Edexcel GCSE Physics 5.3 Black body radiation, covering 5.3.1 Emission of radiation and temperature, 5.3.2 Radiation balance and constant temperature, and 5.3.3 The temperature of the Earth. Each one has a worked solution and a mark scheme showing where the marks go.