Question

describe the working principle of a thermos flask​

Answer 1

Answer:

The thermos flask consists of a double-walled glass vessel resting on a cork inside a metal or plastic case. The outer surface of its inner wall and the inner surface of its outer wall are silvered. The space between the two walls is almost vacuum and the walls are sealed at the top. The flask is placed on a cork in a metal case and is secured at the neck with a ring of rubber. 

Heat from a hot liquid in the thermos flask cannot escape from it by conduction or convection as there is vacuum between the two walls of the glass vessel. The silvered outer surface of the inner wall is a bad radiator and hence it does not radiate heat. At the same time, the silvered inner surface of the outer wall is a good reflector of heat radiation. The materials used to make the thermos flask, namely, glass, cork and rubber between the flask and the container, are all bad conductors of heat. They don't allow the heat to flow out of the flask by conduction or convection.  The insulating stopper or cork at the top minimises heat loss by convection. In the same way, the vacuum between the two walls, rubber, cork and cup on the flask and air do not allow heat from outside to enter into the flask. Thus a thermos flask keeps a hot liquid hot and a cold liquid cold for a long time. 

Explanation:

Answer 2

HELLO MATE

thermos flask has double walls, which are evacuated and the vacuum bottle is silvered on the

inside. The vacuum between the two walls prevents heat being transferred from the inside to the outside

by conduction and convection. With very little air between the walls, there is almost no transfer of heat

from the inner wall to the outer wall by convection. Conduction can only occur at the points where the

two walls meet, at the top of the bottle and through an insulated support at the bottom. The silvered walls

reflect radiated heat back to the inside, the same way a space blanket does. The diagram below shows a

cross section through a thermos.

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