NUMBER $1$

The temperatures at the inner and outer surfaces of the glass cover of a flat plate solar collector placed on the roof of a house are measured to be $31C$ and $25C$ respectively. The glass cover has a surface area of $4m^2$ and a thickness of $0\mathrm{.}6$ cm $.$ The thermal conductivity of the glass is $0\mathrm{.}7\frac{W}{m}C$ and the outside ambient temperature is $15C.$ Heat is lost from the outer surface of the glass cover by convection and radiation with a convection heat transfer coefficient of $15\frac{W}{m^2}K.$ Determine the fraction of heat loss from the glass cover by radiation under steady operating conditions.