Question

Riaz needs a box which can absorb heat from the sun very fast but lose it very slowly. How should the outer and the inner surfaces of the box be coloured so that he gets the best result?

• A. Outer - Silver, Inner - Silver
• B. Outer - Black, Inner - Black
• C. Outer - Silver, Inner - Black
• D. Outer - Black, Inner - Silver

Answer 1

The correct option is D

Outer - Black, Inner - Silver

Dark coloured object absorbs and radiates more heat. Hence, the outer surface should be black as more heat from the sun could be absorbed.
For the inner surface light coloured object absorbs and radiates less heat. Hence, the inner surface should be coated with silver which is both light coloured and polished so that most of the heat is retained by reflecting heat within the box.