Question

9. In a vacuum flask, which methods of heat transfer are prevented by
vacuum?
A) Conduction B) Convection C) Both A and B D) None of these

Answer 1

Answer:

both A and B.

A vacuum flask is a bit like a super-insulated jug. Most versions have an inner chamber and an outer plastic or metal case separated by two layers of glass with a vacuum in between. The glass is usually lined with a reflective metal layer. Unbreakable flasks do away with the glass. Instead, they have two layers of stainless steel with a vacuum and a reflecting layer in between them. There's also a tight, screw-down stopper on the top.

When infrared radiation tries to leave the hot liquid, the reflective lining of the inner chamber reflects it straight back in again. There's virtually no way heat can escape from a vacuum flask and a hot drink stored inside will stay steaming hot for several hours.

hope it helped :)