An optical sensor has a metal casing that is kept at 60 ∘C60\ ^\circ\text{C}60 ∘C inside a cooler test chamber. Energy is transferred between the casing and the chamber only by infrared radiation.
Engineers test two identical casings with different outer surfaces.
| Outer surface | Net energy transferred from the casing by infrared radiation in 1 minute at 60 ∘C60\ ^\circ\text{C}60 ∘C |
|---|---|
| Polished shiny metal | 150 J |
| Matt black | 1650 J |
An electrical heater transfers 150 J of energy to the casing each minute.
Explain why the two surfaces give different values in the table and why the polished shiny casing can remain at 60 ∘C60\ ^\circ\text{C}60 ∘C.
The heater is switched off. Suggest how the rate at which the polished shiny casing emits infrared radiation changes as the casing cools and why its temperature eventually becomes constant.
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.