Question

Four identical copper cylinders are painted. If they are all heated to the same temperature and left in vacuum which will cool most rapidly?

• A. The one painted shiny white
• B. The one painted rough black
• C. The one painted shiny black
• D. The one painted rough white

Answer 1

Answer: (B)

The one painted rough black

Black colour gives maximum absorptivity and emissivity, which we want.
Shiny finish gives maximum reflectivity, which we don't want.
Hence, the answer is painted Rough Black.