Question

A vacuum flask keeps liquids hot for a long time. Explain its effectiveness by describing the molecular activity, or lack thereof, within the vacuum layer. How does this 'empty' space prevent heat transfer? Write your answer in 1-2 sentences.

(2 points)

Answer 1

The vacuum layer contains virtually no molecules, so there are no particle collisions to conduct heat and no medium for convective currents, greatly suppressing those modes of heat transfer. Any remaining heat loss is by thermal radiation, which is reduced by the flask's reflective inner surfaces.