Thermal Energy Transfer: Question 10
Syllabus 2.3.3
A clothing company is designing outdoor jackets: one range for a hot, sunny desert country, and another range for a cold, snowy mountain country. Both types of jacket are worn outdoors in direct sunlight for long periods.
Which choice of jacket colour correctly applies the effect of surface colour on thermal radiation?
Show worked solution Hide worked solution
Worked solution
Step 1: Recall the rule for surface colour and radiation
Dull, dark surfaces absorb infrared radiation well, while light-coloured, shiny surfaces reflect most of the radiation that reaches them and absorb far less.
Step 2: Apply this to the desert jackets
In the hot, sunny desert country, the goal is to keep the wearer cool, so the jacket should absorb as little of the Sun’s radiation as possible. A light-coloured (or white) jacket reflects most of the incoming radiation rather than absorbing it, keeping the wearer cooler.
Step 3: Apply this to the mountain jackets
In the cold, snowy mountain country, the goal is to keep the wearer warm, so the jacket should absorb as much of the Sun’s radiation as possible. A dark-coloured jacket absorbs radiation well, helping to warm the wearer using the available sunlight.
Step 4: Match to the correct option
Light colours for the desert range and dark colours for the mountain range, for the reasons above, is exactly option A.
Why the other options are wrong
| Option | Error |
|---|---|
| B | Reverses the rule: dark colours actually absorb radiation well (not reflect it), and light colours reflect radiation well (not absorb it). |
| C | Ignores the genuine effect of surface colour on radiation absorption; colour matters in addition to fabric thickness. |
| D | Confuses the radiation effect of colour with insulation against conduction; colour affects radiation absorption, not how well a fabric resists conduction. |
Final answers
- Light-coloured jackets for the desert range (absorb less radiation, stay cooler) and dark-coloured jackets for the mountain range (absorb more radiation, stay warmer), option A.