Waves Practice Problem Set Worksheet Page 31
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ECHANICS
RACTICE
ROBLEM
ETS
2
36.1°C and her body cross-sectional area is about 1.15 m
. If the thermal conductivity
of wool is 0.04 W/(m•K) and the rate of heat loss by conduction through her clothing
is 314 W, what is the temperature outside?
Answer: 4°C
12. The operating temperature of a tungsten filament in an incandescent light bulb is
2177°C. and its emissivity is 0.35. Find the surface area of the filament of a 150-W
light bulb if all the electrical energy is radiated by the filament as electromagnetic
-4
2
waves into a room at 21°C.
Answer: 3.4 x 10
m
13. A very thin square steel plate, 10 cm on a side, is heated in a blacksmith’s forge to a
temperature of 800°C. If the emissivity is 0.60, what is the total ideal rate of radiation
of energy?
Answer: 450 W
a. If thin square steel plate is put into a room that is 30°C, what is the net flow of
heat by radiation?
Answer: 448 W
11. (G13.9) A concrete highway is built of slabs 14 m long at 20°C. How wide should
the expansion cracks between the slabs be at 20°C to prevent buckling if the range of
temperatures is -30°C to +50°C? The coefficient of linear expansion for concrete is 12
-6
-1
x 10
°C
.
Answer: 0.50 cm
12. (G14.E11) A major source of heat loss from a house is through the windows.
Calculate the rate of heat flow through a glass window of 2.0 m x 1.5 m that is 3.2
mm thick, if the temperatures of the inner and outer surfaces are 15.0°C and 14.0°C,
respectively.
Answer: 790 W
13. (G14.33) How much power is radiated by a tungsten sphere (e = 0.35) of radius 22
cm at a temperature of 25°C?
Answer: 95 W
Gamzon & Gregorian-Michaelsen
6/7/16
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