Question

Question 7. A substance remains in the same temperature in a thermos flask or vacuum bottle. Now observe the following diagram of a thermos flask.What purpose does the vacuum compartment in the thermos flask serve? Stopper Vacuum Double glass shell Silver coating Casting
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Answer 1

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 .

(d) a plastic (or metal) case is provided with a flask , to protect the flask from physical damage .

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