Shiny coatings and radiation
Question: How does the shiny outside coating on the jug reduce heat
loss?
Answer:
Heat energy loss from an object depends on three
things:
(a) the difference in temperature between the surface and the
surroundings
(b) the area of the surface
(c) the nature of the surface (whether it is
rough, shiny, black, white etc.)
You wanted to know about the last
one.
Rough matt black surfaces are the best radiators of heat energy at a given
temperature.
Shiny surfaces do not radiate well and so they lose much less heat
energy than a black jug at the same temperature. Therefore the shiny coating on the outside
of your jug helps to keep the jug warm. (the quantity to look up in advanced books is
emissivity and see how it relates to the Stefan-Boltzmann Law).
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