Question

8.
In a thermos flask, heat loss due to
conduction is prevented because
(i) glass and cork are poor conductors of
heat
(ii) conduction cannot take place in
vacuum as it requires a medium
(iii) the stopper and the vacuum prevent
heat loss because of absence of air
(iv) the highly polished silver walls prevent
heat loss
a) (i) and (ii)
c) (iii) and (iv)
b) (ii) and (iii)
d) (i) and (iv)​

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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Answer 2

Answer:

b)

Explanation:

because they prevent heat