How does a vacuum flask, commonly called a thermos, keep drinks hot or cold for extended periods?

Explanation

A vacuum flask keeps liquids hot or cold by using a double-walled container with a vacuum, meaning empty space, between the walls, which greatly reduces heat transfer through conduction and convection since there are few or no particles to carry heat across the gap. The inner surface is often silvered to reflect radiant heat back toward the liquid. Together, these design features slow down heat loss or gain, keeping the contents at a stable temperature for hours. Explore more Everyday Science MCQs on mcqstutor to keep practicing.