Determine how many times greater heat loss occurs through a glass window that is

Question

Determine how many times greater heat loss occurs through a glass window that is 80.0 cm high, 70 cm wide, and 0.300 cm thick (k= 0.791 W/m C) than a electrical supply line running outside to an exterior mounted light. This 30.0 em long supply line consisting of three copper wires, each 1.50 mm in diameter, that are well insulated and only exposed at the very ends of each wire. The thermal conductivity of copper is 395 W/mCelcious. Hint: Since this problem is a direct comparison, it really won't make any difference what you choose for inside and outside temperatures.

Explanation / Answer

Area = (.8 m)•(.7 m) = .56 m2. We will also need to give attention to the unit on thickness (d). It is given in units of cm; we will need to convert to units of meters in order for the units to be consistent with that of k and A. d = 1.5 mm = 0.0015 m Now we are ready to calculate the rate of heat transfer by substitution of known values into the above equation. Rate = (0.395 W/m/°C)•(.56 m2)•(30°C)/(0.0015 m) Rate = 4424 W

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