d.
0.036 kg/m3
e.
0.04 kg/m3
42. Air at a temperature of 32° F has a relative humidity of 60%. If the temperature of the same
air rises to 40° F, the relative humidity
a.
stays the same
b.
increases
c.
decreases
d.
cannot be determined
43. Even when the temperature of a pan of water is below the boiling point, some water still
evaporates. This is because
a.
of convection
b.
the kinetic energies of individual water molecules vary above and below the
average value
c.
the humidity always increases
d.
none of the above
44. In a steam engine, steam at 140°C in a turbine does work on an external system, and the
steam leaves the turbine at 100°C. The efficiency of the steam engine is 5%. The relevant
physical principle is
a.
the first law of thermodynamics
b.
the second law of thermodynamics
c.
specific heat capacity
d.
operation of a heat pump
e.
none of the above
45. The efficiency of a heat engine
a.
can never exceed the Carnot efficiency
b.
can be improved by lowering the temperature of the cool reservoir
c.
can be improved by raising the temperature of the hot reservoir
d.
all of the above
46. A piston compresses a gas, while at the same time heat is lost to the surroundings. The
temperature of the gas rises. The amount of temperature rise is governed by
a.
the first law of thermodynamics
b.
the second law of thermodynamics
c.
specific heat capacity
d.
a heat pump
e.
none of the above
47. Heat transfer by radiation occurs via
a.
electromagnetic waves
b.
nuclear decay
c.
molecular collisions
d.
the solar wind
e.
none of the above
48. Heat flows from
a.
cold to hot
c.
Kelvin to Celsius
b.
hot to cold
d.
the same as temperature
49. As long as there is ice in your drink, the temperature of the ice remains near
a.
room temperature
c.
zero Celsius
b.
the temperature of the drink
d.
zero Fahrenheit
50. A car weighs 1,725 kg and is speeding on I-75 at 90 miles per hour. The brake rotors are
made of 20 kg of iron and steel composite. The car comes to the crest of a hill and traffic is
stopped ahead. The driver slams on the brakes and stops the car just in time. What is the
temperature change in the rotors?
a.
180 oC
c.
251.7 oF
b.
151.7 oC
d.
300 K
51. The specific heat capacity of a substance is the amount of energy required to raise 1 kg of
the substance by a temperature of
a.
1°F
c.
10 °F
b.
10 °C
d.
1°C
52. In the First Law of Thermodynamics, the work can be
a.
only positive
c.
neither
b.
only negative
d.
either positive or negative
MULTIPLE RESPONSE
1. Absolute zero is
a.
0 K
c.
– 273.15°C
b.
– 459.67°F
d.
0 on any temperature scale.
2. Stepping barefoot off a rug onto a hardwood floor makes your feet feel cold. Why?
a.
The hardwood floor is at a lower temperature than the rug.
b.
The hardwood floor is at a lower temperature than your feet.
c.
The hardwood floor conducts heat away from your feet better than the rug.
d.
all of the above
3. Solar energy
a.
is a recent invention
b.
has been used for a long time
c.
has not yet been successfully developed
d.
is indirectly the source of most of the energy we use
4. The internal energy of air can be increased by
a.
compressing it
c.
lifting it
b.
allowing heat to flow into it
d.
allowing it to expand
5. The internal energy of a substance can be increased by
a.
doing work on it
b.
letting it do work
c.
adding heat to it
d.
extracting heat from it
e.
none of the above
6. Internal energy in a system can be changes by
a.
doing work on the system
c.
changing the temperature of the system
b.
increasing the specific heat in the
system
d.
transferring heat to/from the system
COMPLETION
1. The average kinetic energy of the atoms in a spoon determines its __________.
2. The first law of thermodynamics is basically a special version of the law of
______________.
3. Two devices that make use of a bimetallic strip are a __________ and a __________.
4. A bimetallic strip is formed from two materials that have different __________.
5. The lowest temperature is called ______________.
6. The temperature scale where the numerical value is proportional to the average kinetic
energy of the atoms or molecules is __________.
7. You hold one end of a solid rod in a fire, and the other end becomes hot. This is an example
of __________.
8. The warmth you feel from the sun at the beach is an example of __________.
9. A wood stove in the corner of a cabin causes the entire cabin to become heated. This is an
example of __________.
10. As the air cools at night the relative humidity usually __________.
11. A hot pizza contains __________.
12. Heating the air in a hot air balloon reduces the air’s _________.
13. A bimetallic strip is usable as a thermometer because of the property of __________.
14. Three examples of a heat mover are __________, __________, and __________.
15. Two ways that the internal energy of a substance can be increased are __________ and
__________.
16. __________ is transferred from a substance if it is exposed to something that has a lower
temperature.
17. The coefficient of linear expansion of ordinary glass is three times that of Pyrex glass. An
ordinary glass rod and a Pyrex glass rod of equal lengths at room temperature are dropped
into boiling water. The change in length of the ordinary glass rod will be __________ times
the change in length of the Pyrex glass rod.
18. The specific heat capacity of copper is three times the specific heat capacity of lead. Equal
masses of copper and lead are heated from room temperature to the temperature of boiling
water. To achieve this, the amount of heat added to the copper is __________ times the
amount of heat added to the lead.
19. When ice melts, its temperature __________.
20. When water boils, its temperature __________.
21. The specific heat capacity of water is about twice the specific heat capacity of ice. The
amount of heat required to raise the temperature of 1 kg of water 10°C is __________ times
the amount of heat required to raise the temperature of 1 kg of ice 10°C.
22. The latent heat of vaporization of water is roughly 10 times the latent heat of fusion of
water. The amount of heat required to boil 1 kg of water is __________ times the amount of
heat required to melt 1 kg of ice.
23. Two ways that the temperature of a gas can be increased are by __________ and
__________.
24. Natural processes tend to increase the __________ of thermodynamic systems.
25. A 1 kg block of ice is removed from a freezer where its temperature was –10°C. The amount
of heat absorbed by the ice as it warms to 0°C is __________.
26. The 1 kg block of ice melts into water. The amount of heat absorbed by the ice as it melts is
__________.
27. As the ice is melting, the temperature of the ice-water mixture rises by __________.
28. After the 1 kg block of ice melts, the amount of heat required to raise its temperature to
10°C is __________.
29. The Eiffel tower in Paris is made primarily of iron, whose coefficient of linear expansion is
about 10 x 10-6/°C. On a cold day when the temperature is –10°C the Eiffel tower is 300
meters tall. Its height on a hot day when the temperature is 40°C is __________.
30. At 96°F the saturation density of air is 0.04 kg/m3. If the weather report says the relative
humidity is 90% when the temperature is 96°F, the humidity is __________.
31. In a steam engine, steam at 140°C in a turbine does work on an external system, and the
steam leaves the turbine at 100°C. The efficiency of the steam engine is 5%. The relevant
physical principle is the __________ law of thermodynamics.
32. The air temperature where the humidity reaches the saturation density is called the
___________.
33. A piston compresses a gas, while at the same time heat is lost to the surroundings. The
temperature of the gas rises. This is governed by the __________ law of thermodynamics.
34. A material through which heat conducts slowly is called a __________.
35. An object transfers heat when its temperature is raised by contact with a
36. An object transfers heat when its temperature is lowered by contact with
37. At temperatures below their boiling point, liquids gradually go into the gas phase through a
process called
MATCHING
Match each item with the correct statement below.
a.
bimetallic strip
i.
heat mover
b.
Carnot efficiency
j.
humidity
c.
conduction
k.
internal energy
d.
convection
l.
radiation
e.
entropy
m.
saturation density
f.
evaporation
n.
temperature
g.
heat
o.
dew point
h.
heat engine
1. used in thermostats and some thermometers
2. can be increased by doing work on a substance or by adding heat to it
3. main mechanism of heat transfer in a solid
4. the density of water vapor in the air
5. this is how we receive heat from the sun
6. refrigerators, air conditioners and heat pumps are examples
7. the maximum possible humidity
8. the best that a heat engine can have
9. heat transfer by way of buoyant mixing in a fluid
10. depends on the average kinetic energy of atoms and molecules in a substance
11. At temperatures below their boiling point, liquids gradually go into the gas phase through a
process called
PROBLEM
1. The Eiffel tower in Paris is 300 meters tall on a cold day (T = – 5 degrees Celsius). What is
its height on a hot day when the temperature is 35 degrees? (It is made of iron which has a
coefficient of linear expansion of 0.000012 per degree Celsius.)
2. The air inside a bicycle tire pump has 60 joules of work done on it as 20 joules of heat is
conducted away from it. What is the change in internal energy of the air?
3. A 4 kilogram block of ice is removed from a freezer where its temperature was maintained
at –20 degrees Celsius. How much heat does the ice absorb as it is warmed to –10 degrees?
(The specific heat capacity of ice is 2,000 joules per kilogram degree Celsius.)
4. A baseball with mass 0.14 kilograms and speed 40 m/s is caught. If all of its kinetic energy
is converted to internal energy as it is caught, what is its temperature change? (Assume the
baseball’s specific heat capacity is 1,000 joules per kilogram degree Celsius.)
5. On a winter day the temperature is 5 degrees Celsius and the humidity is 0.003 kilograms
per cubic meter.
(a) What is the relative humidity?
(b) The air is brought into a building and heated to 20 degrees Celsius without changing the
humidity. What is the relative humidity inside the building?
6. What is the maximum efficiency of a heat engine operating between 293 Kelvins and 273
Kelvins, the temperatures at the surface and several hundred meters below the surface,
respectively, of the ocean?
7. An aluminum wing on a plane is 38 m long when the temperature is 20 oC. At what
temperature (in oC) would the wing be 0.04 m shorter? Enter your answer to one decimal
place. You should think about the physics of the situation before trying to solve the
problem. (Hint: You are being asked for a temperature, not a temperature change).