Energy conservation is important for houses. to what fraction is the heat transfer rate reduced by replacing a glass window 3 ft wide and 5 ft high with a smaller window 2 ft wide by 3 ft high? as a typical case, assume the outside temperature in the winter is 25°f and the inside temperature is 75°f. for this example assume u = 5.5 btu/(hr)(ft2)(°f)

Explanation:

Given

Initial Area of glass window is

Area of second window

And Heat transfer is given by

where k=thermal conductivity

dT=Temperature difference

dx=Thickness

Assuming k,\Delta T and thickness remains same

----1

----2

dividing 1 & 2

Thus

Thus heat is reduced by 60 %

the duration of a photographic flash is related to an rc time constant, which is 0.100 μs for a certain camera.