Give reasons for the following: In a thermos flask, [3] i) A vacuum is created between the two walls of the glass bottle ii) The two walls of glass bottle are silvered on their vacuum side. iii) The glass bottle is covered with a cork stopper.
Answers
Answer:
In a thermos flask ,
(a) a thin layer of vacuum is provided between the two walls of flask, to minimise the heat loss by conduction , because for conduction medium (molecules) is required , but now medium is absent .
.(b) the two walls are silvered to minimise the heat loss by radiation , because a shiny surface is a bad absorber and bad emitter of radiation i.e. good reflector of heat , so prevents the heat exchange between content of flask and surrounding .
(c) the lid of flask is provided with a tight cork stopper to minimise the heat loss by convection , so that convection currents cannot go out .
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