A manufacturer compares two surface finishes for steel components that must cool quickly after heating.
The components have the same mass, dimensions and material. They differ only in surface finish. They are heated to the same temperature and placed side by side in a room at 20 ∘C20\ ^{\circ}\text{C}20 ∘C.
The table shows the mean results from repeated tests.
| Surface finish | Starting temperature in ∘C^{\circ}\text{C}∘C | Final temperature in ∘C^{\circ}\text{C}∘C | Time taken in s\text{s}s |
|---|---|---|---|
| matt black | 90 | 60 | 300 |
| shiny silver | 90 | 60 | 750 |
Calculate the mean temperature decrease per second for each component.
Explain how the results support the choice of the matt black finish for components that must cool quickly.
At one stage, the matt black component absorbs 1.8 kJ and emits 3.0 kJ of radiation in 150 s.
Calculate the average net power transferred from the component by radiation.
The table shows the average powers absorbed and emitted by the matt black component as it cools.
| Temperature in ∘C^{\circ}\text{C}∘C | Average power absorbed in W\text{W}W | Average power emitted in W\text{W}W |
|---|---|---|
| 60 | 12 | 20 |
| 45 | 12 | 17 |
| 30 | 12 | 14 |
| 20 | 12 | 12 |
Using the data, explain how the temperature of the component changes from 60 ∘C60\ ^{\circ}\text{C}60 ∘C until it becomes constant.
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.