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cm thick. The inside temperature of what percentage saving in fuel can is conducted through a combined
the door is 20.0 0C and the outside the home owner realize? glass window and storm window in
temperature of the door is -5.00 0C. 16. If the internal temperature 8.00 hr if the window is 81.0 cm
of the human body is 37.0 0C, the wide by 114 cm high and 0.318 cm
16-24 Vibratory Motion, Wave Motion and Fluids
thick? The storm window is the 2.50 m high and 3.00 m wide, at a
same size but is separated from the temperature of 20.0 0C? What is the
inside window by an air gap of 5.00 wavelength of the maximum
cm. The temperature of the inside intensity of radiation?
window is 20.0 C and the 30. A blackbody initially at
temperature of the outside window 100 0C is heated to 300 0C. How
is -7.00 0C. Treat the combination much more power is radiated at the
Diagram for problem 36.
as a compound wall. higher temperature?
31. A blackbody is at a
37. Find the amount of thermal
16.4 Radiation temperature of 200 0C. Find the
energy conducted through a wall,
23. How much thermal energy wavelength of the maximum
5.00 m high, 12.0 m long, and 5.00
from the sun falls on the surface of intensity of radiation.
cm thick, if the wall is made of
the earth during an 8-hr period? 32. A blackbody is radiating at
(a) concrete, (b) brick, (c) wood, and
(Ignore reflected solar radiation a temperature of 300 K. To what
(d) glass. The temperature of the
from clouds that does not make it to temperature should the body be
hot wall is 25.0 0C and the cold wall
the surface of the earth.) raised to double the amount of
-5.00 0C.
radiation?
*38. Show that the distribution
33. A distant star appears red,
of solar energy over the surface of
with a wavelength 7.000 × 10-7 m.
the earth is a function of the
What is the surface temperature of
latitude angle Æ. Find the energy
that star?
per unit area per unit time hitting
the surface of the earth during the
Additional Problems
vernal equinox and during the
34. An aluminum pot contains
summer solstice at (a) the equator,
10.0 kg of water at 100 0C. The
(b) 30.00 north latitude, (c) 45.00
bottom of the pot is 15.0 cm in
north latitude, (d) 60.00 north
Diagram for problem 23.
radius and is 3.00 mm thick. If the
latitude, and (e) 90.00 north
bottom of the pot is in contact with
latitude. At the vernal equinox the
24. If the mean temperature of
a flame at a temperature of 170 0C,
sun is directly overhead at the
the surface of the earth is 288 K,
how much water will boil per
equator, whereas at the summer
how much thermal energy is
minute?
solstice the sun is directly overhead
radiated into space per second?
35. Find how much energy is
at 23.50 north latitude.
25. Assuming the human body
lost in one day through a concrete
has an emissivity, e = 1, and an
slab floor on which the den of a
area of approximately 2.23 m2, find
house is built. The den is 5.00 m
the amount of thermal energy
wide and 6.00 m long, and the slab
radiated by the body in 8 hr if the
is 15.0 cm thick. The temperature of
surface temperature is 95.0 0F.
the ground is 3.00 0C and the
26. If the surface temperature
temperature of the room is 22.0 0C.
of the human body is 35.0 0C, find
36. A lead bar 2.00 cm by 2.00
the wavelength of the maximum
cm and 10.0 cm long is welded end
intensity of radiation from the
to end to a copper bar 2.00 cm by
human body. Compare this
2.00 cm by 25.0 cm long. Both bars
wavelength to the wavelengths of
are insulated from the
visible light.
environment. The end of the copper
27. How much energy is
bar is placed in a steam bath while
radiated per second by an
the end of the lead bar is placed in
aluminum sphere 5.00 cm in radius,
an ice bath. What is the
at a temperature of (a) 20.0 0C, and
temperature T at the interface of
(b) 200 0C? Assume that the sphere
the copper-lead bar? How much
emits as a blackbody. Diagram for problem 38.
thermal energy flows through the
28. How much energy is
bar per minute?
radiated per second by an iron 39. An asphalt driveway, 50.0
cylinder 5.00 cm in radius and 10.0 m2 in area and 6.00 cm thick,
cm long, at a temperature of receives energy from the sun. Using
(a) 20.0 0C and (b) 200 0C? Assume the solar constant of 1.38 × 103
blackbody radiation. W/m2, find the maximum change in
29. How much energy is temperature of the asphalt if (a) the
radiated per second from a wall radiation from the sun hits the
Chapter 16 Heat Transfer 16-25
driveway normally for a 2.00-hr how much water must boil per
period and (b) the radiation from minute to cool the engine?
the sun hits the driveway at an *45. When the surface through
angle of 350 for the same 2.00-hr which thermal energy flows is not
period. Take the density of asphalt flat, such as in figure 16.6, the
to be 1219 kg/m3 and the specific equation for heat transfer, equation
heat of asphalt to be 4270 J/kg 0C. 16.10, is no longer accurate. With
*40. Find the amount of the help of the calculus it can be
radiation from the sun that falls on shown that the amount of thermal
Diagram for problem 46.
the planets (a) Mercury, (b) Venus, energy that flows through the sides
(c) Mars, (d) Jupiter, and (e) Saturn of a rectangular annular cylinder is
*47. Show that for large values
in units of W/m2. given by
of r and r the solution for thermal
1 2
41. If the Kelvin temperature of "Q = 2Àkl"T
energy flow through a spherical
a blackbody is quadrupled, what "t ln(r /r )
2 1
shell (problem 46) reduces to the
happens to the rate of energy
solution for the thermal energy flow
radiation?
where l is the length of the cylinder,
through a flat slab.
*42. A house measures 12.0 m
r is the inside radius of the
1
*48. In problems 45 and 46
by 9.00 m by 2.44 m high. The walls
cylinder, and r is the outside
2
assume that you can use the
contain 10.0 cm of glass wool.
radius of the cylinder. Steam at
formula for the thermal energy flow
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