An engineering company tests two identical metal moulds, M and N. The outer surface of one mould is matt black and the outer surface of the other is polished. The matt black surface is a good absorber of infrared radiation.
Each mould is heated to three different temperatures. A detector records the energy emitted as infrared radiation in 20 seconds.
| Temperature | Energy emitted by M in 20 seconds | Energy emitted by N in 20 seconds |
|---|---|---|
| 300 ∘C300\ ^\circ\text{C}300 ∘C | 12.0 kJ | 3.0 kJ |
| 200 ∘C200\ ^\circ\text{C}200 ∘C | 5.8 kJ | 1.5 kJ |
| 100 ∘C100\ ^\circ\text{C}100 ∘C | 2.2 kJ | 0.6 kJ |
Both moulds are then heated to 300 ∘C300\ ^\circ\text{C}300 ∘C and placed in a cold chamber. Radiation absorbed by either mould from the chamber is negligible.
Explain which mould has the matt black surface and predict which mould will cool to 100 ∘C100\ ^\circ\text{C}100 ∘C first. Use the data in the table.
106 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.