b$)$ Heat flows due to a temperature difference between two regions. Describe the

three principal mechanisms of heat flow and give an example of a device

designed to minimise all three. $(6$ marks$)$

One of the windows in a house has the shape of a square $2\mathrm{.}0$ m per side. The

glass in the window is $0\mathrm{.}30$ cm thick.

i$)$ What is the rate of heat loss through the window and how much heat

escapes during one day if the temperature inside is $22$oC and that outside

is $5\mathrm{.}0$oC$?$ The thermal conductivity of glass is $0\mathrm{.}84$ W$/$m$/$K$.(2$ marks$)$

ii$)$ What is the physical reason that double glazing reduces this loss of heat so

dramatically?