Question

A vacuum flask has shiny surfaces on the vacuum side to

• A. prevent heat loss.
• B. increase heat loss.
• C. prevent heat gain.
• D. increase heat gain.

Answer 1

The correct option is A prevent heat loss.

Black surfaces are good absorbers and radiators of heat radiations. Painted vacuum flask black on the vacuum side allows to contain more heat inside the flask and keep its contents hotter longer.