A vacuum flask is an insulating storage vessel that greatly lengthens the time over which its contents remain hotter or cooler than the flask's surroundings. Invented by Sir James Dewar in 1892, the vacuum flask consists of two flasks, placed one within the other and joined at the neck.

What is thermos flask for Class 7?

A thermos flask or a vacuum flask is used to keep a hot liquid hot and a cold liquid cold for a long time, by preventing the loss or gain of heat energy due to conduction, convection and radiation. ... The silvered outer surface of the inner wall is a bad radiator and hence it does not radiate heat.

What do you mean by thermos flask?

Definitions of thermos flask. vacuum flask that preserves temperature of hot or cold drinks. synonyms: thermos, thermos bottle. type of: vacuum bottle, vacuum flask. flask with double walls separated by vacuum; used to maintain substances at high or low temperatures.