Question

In a thermos flask, what prevents heat loss
(a) radiation
(b) heat losses by conduction and convection are largely prevented

Answer 1

The heat loss is prevented by radiation, conduction and convection processes as
(a) Coating of both the inner walls of glass with shiny bright silvering. The heat radiations are reflected back by the silvery surface.
(b) The vacuum created by pumping out all the air prevents heat loss by conduction and convection.