Physics - Heat & Thermo Question with Solution | TestHub

A manufacturer is able to offer two models of heat-conserving windows, as described below. Window A is a simple pane of glass, 4 mm thick. Window B, on the other hand, consists of two extremely thin panes of glass, separated by an air gap of 2mm, as shown in the figure below. If the thermal conductivity of glass is known to be $0.8{\mathrm{Wm}}^{-1}{\mathrm{K}}^{-1}$ and that of air is $0.025{\mathrm{Wm}}^{-1}{\mathrm{K}}^{-1}$, then the ratio of heat flow ${\mathrm{Q}}_{\mathrm{A}}$ through Window A to the heat flow ${\mathrm{Q}}_{\mathrm{B}}$ through Window B is given by $\frac{{\mathrm{Q}}_{\mathrm{A}}}{{\mathrm{Q}}_{\mathrm{B}}}=$