Draw a labelled diagram of a thermosflask.Answer the following:
a)Why is air removed from space between the two walls of glass bottle?
b)Why is the glass bottle held in a place inside the metal case with the help of cork pieces.?
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 .
(d) a plastic (or metal) case is provided with a flask , to protect the flask from physical damage .
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