1. Heat
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2. This lecture will help you understand:
The Kinetic Theory of Matter
Temperature
Absolute Zero
What Is Heat?
Quantity of Heat
The Laws of Thermodynamics
Entropy
Specific Heat Capacity
Thermal Expansion
Expansion of Water
Heat Transfer: Conduction
Heat Transfer: Convection
Heat Transfer: Radiation
Emission of Radiant Energy
Absorption of Radiant Energy
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3. The Kinetic Theory of Matter
Matter is made up of tiny particles (atoms or molecules) that are always in motion.
Thermal energy:
The total energy (kinetic and potential) of the submicroscopic particles that make up a substance.
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4. Temperature Temperature
is the measure of hotness or coldness of an object (degrees Celsius, or degrees Fahrenheit, or kelvins).
is related to the average translational kinetic energy per molecule in a substance.
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5. Temperature
A thermometer is an instrument that measures temperature by comparing the expansion and contraction of a liquid as it gains or loses thermal energy.
An infrared thermometer measures temperature by the radiation a substance emits.
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6. Temperature Temperature has no upper limit.
The temperature of a substance is registered on a liquid-base thermometer when the substance has reached thermal equilibrium with the thermometer.
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7. Temperature
Three temperature scales differ in zero point and divisions:
Celsius scale
freezing point of water: 0C
boiling point of water: 100C
division: 100 degree units
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8. Temperature
Fahrenheit scale freezing point of water: 32F boiling point of water: 212F division: 180 degree units
Kelvin scale (used in scientific research) freezing point of water: 273 K boiling point of water: 373 K division: same-size increments as Celsius scale
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9. Temperature CHECK YOUR NEIGHBOR
There is twice as much molecular kinetic energy in
2 liters of boiling water as in 1 liter of boiling water.
Which is the same for both?
Temperature
Thermal energy
Both temperature and thermal energy
Neither temperature nor thermal energy
Explain your answer to your neighbor.
A. Temperature.
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10. Temperature CHECK YOUR ANSWER
There is twice as much molecular kinetic energy in
2 liters of boiling water as in 1 liter of boiling water.
Which is the same for both?
Temperature
Thermal energy
Both temperature and thermal energy
Neither temperature nor thermal energy
Explanation:
The average kinetic energy of the molecules is the
same, which means that the temperature is the same for
both.
A. Temperature.
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11. Absolute Zero
Absolute zero or zero K is the lowest limit of temperature at –273C where molecules have lost all available kinetic energy. A substance cannot get any colder.
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12. What Is Heat?
Heat is defined as a flow of thermal energy due to a temperature difference.
The direction of heat flow is from a higher-temperature substance to a lower-temperature substance.
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13. What Is Heat? CHECK YOUR NEIGHBOR
If a red-hot thumbtack is immersed in warm water,
the direction of heat flow will be from the
warm water to the red-hot thumbtack.
red-hot thumbtack to the warm water.
There is no heat flow.
There is not enough information.
Explain your answer to your neighbor.
B. red hot thumbtack to the warm water.
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14. What Is Heat? CHECK YOUR ANSWER
If a red-hot thumbtack is immersed in warm water,
the direction of heat flow will be from the
warm water to the red-hot thumbtack.
red-hot thumbtack to the warm water.
There is no heat flow.
There is not enough information.
B. red hot thumbtack to the warm water.
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15. Quantity of Heat Heat is measured in units of energy—joules or
calories.
A calorie is defined as the amount of heat needed to
raise the temperature of 1 gram of water by 1 Celsius
degree.
4.19 joules = 1 calorie
so 4.19 joules of heat will change the temperature
of 1 gram of water by 1 Celsius degree.
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16. Quantity of Heat
The energy rating of food and fuel is measured by the energy released when they are metabolized.
The heat unit for labeling food is the kilocalorie.
One kilocalorie or Calorie (with a capital C) is the heat needed to change the temperature of 1 kilogram of water by 1 degree Celsius.
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17. Quantity of Heat CHECK YOUR NEIGHBOR
The same quantity of heat is added to different
amounts of water in two equal-size containers. The
temperature of the smaller amount of water
decreases more.
increases more.
does not change.
There is not enough information.
Explain your answer to your neighbor.
B. increases more.
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18. Quantity of Heat CHECK YOUR ANSWER
The same quantity of heat is added to different
amounts of water in two equal-size containers. The
temperature of the smaller amount of water
decreases more.
increases more.
does not change.
There is not enough information.
B. increases more.
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19. Quantity of Heat CHECK YOUR NEIGHBOR
You heat a half cup of tea and its temperature
rises by 4C. How much will the temperature rise if
you add the same amount of heat to a full cup of tea?
0C
2C
4C
8C
Explain your answer to your neighbor.
B. 2C.
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20. Quantity of Heat CHECK YOUR ANSWER
You heat a half cup of tea and its temperature
rises by 4C. How much will the temperature rise if
you add the same amount of heat to a full cup of tea?
0C
2C
4C
8C
B. 2C.
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21. The Laws of Thermodynamics
First law of thermodynamics:
Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred.
When thermal energy transfers as heat, it does so with no net loss or gain.
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22. The Laws of Thermodynamics
Second law of thermodynamics:
Heat never spontaneously flows from a lower-temperature substance to a higher temperature substance.
Heat can be made to flow the opposite way only when work is done on the system or when energy is added from another source.
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23. The Laws of Thermodynamics
Third law of thermodynamics:
No system can reach absolute zero.
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24. The Laws of Thermodynamics CHECK YOUR NEIGHBOR
When work is done on a system–compressing air in a tire
pump, for example–the temperature of the system
increases.
decreases.
remains unchanged.
is no longer evident.
Explain your answer to your neighbor.
A. increases.
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25. The Laws of Thermodynamics CHECK YOUR ANSWER
When work is done on a system–compressing air in a tire
pump, for example–the temperature of the system
increases.
decreases.
remains unchanged.
is no longer evident.
Explanation:
In accord with the first law of thermodynamics, work input
increases the energy of the system.
A. increases.
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26. Entropy Entropy is a measure of the disorder of a system.
Whenever energy freely transforms from one form into another, the direction of transformation is toward a state of greater disorder and, therefore, toward one of greater entropy.
Greater disorder  higher entropy
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27. Entropy Second law of thermodynamics — a restatement:
Natural systems tend to disperse from concentrated and organized energy states toward diffuse and disorganized states.
Energy tends to degrade and disperse with time.
The total amount of entropy in any system tends to increase with time.
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28. Entropy CHECK YOUR NEIGHBOR
Your room gets messier each week. In this case, the
entropyof your room is
increasing.
decreasing.
hanging steady.
nonexistent.
Explain your answer to your neighbor.
A. increasing.
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29. Entropy CHECK YOUR ANSWER
Your room gets messier each week. In this case, the
entropy of your room is
increasing.
decreasing.
hanging steady.
nonexistent.
Comment:
If your room became more organized each week, then entropy
would decrease in proportion to the effort expended.
A. increasing.
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30. Specific Heat Capacity
The specific heat capacity is the quantity of heat required to change the temperature of 1 unit mass of a substance by 1 degree Celsius.
Specific heat capacity is
thermal inertia that indicates the resistance of a substance to a change in temperature.
sometimes called specific heat.
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31. Specific Heat Capacity CHECK YOUR NEIGHBOR
Which has a higher specific heat capacity: water or land?
Water
Land
Both of the above are the same.
None of the above
Explain your answer to your neighbor.
A. Water.
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32. Specific Heat Capacity CHECK YOUR ANSWER
Which has a higher specific heat capacity: water or land?
Water
Land
Both of the above are the same.
None of the above
Explanation:
A substance with small temperature changes for large heat
changes has a high specific heat capacity. Water takes
much longer to heat up in the sunshine than does land.
This difference has a major influence on climate.
A. Water.
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33. Thermal Expansion
When the temperature of a substance is increased, its particles jiggle faster and move farther apart.
All forms of matter generally expand when heated and contract when cooled.
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34. Thermal Expansion CHECK YOUR NEIGHBOR
When telephone lines are strung between poles in the
summer, it is advisable for the lines to
sag.
be taut.
be close to the ground.
allow ample space for birds.
Explain your answer to your neighbor.
A. sag.
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35. Thermal Expansion CHECK YOUR ANSWER
When telephone lines are strung between poles in the
summer, it is advisable for the lines to
sag.
be taut.
be close to the ground.
allow ample space for birds.
Explanation:
Telephone lines are longer in a warm summer and shorter in a cold
winter. Hence, they sag more on hot summer days than during the winter.
If the lines are not strung with enough sag in the summer, they might
contract too much and snap during the winter—especially when they are
covered with ice.
A. sag.
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36. Expansion of Water
When water becomes ice, it expands. Ice has open-structured crystals resulting from strong bonds at certain angles that increase its volume. This make ice less dense than water.
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37. Expansion of Water
Water between 0C and 4C does not expand with temperature. As the temperature of 0 water rises, the water contracts until it reaches 4C. Thereafter, it expands.
Water is at its smallest volume and greatest density at 4C. When 0C water freezes to become ice, however, it has its largest volume and lowest density.
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38. Expansion of Water Volume changes for a 1-gram sample of water:
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39. Expansion of Water CHECK YOUR NEIGHBOR
When a sample of 0C water is heated, it first
expands.
contracts.
remains unchanged.
There is not enough information.
Explain your answer to your neighbor.
B. contracts.
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40. Expansion of Water CHECK YOUR ANSWER
When a sample of 0C water is heated, it first
expands.
contracts.
remains unchanged.
There is not enough information.
Explanation:
Water continues to contract until it reaches a
temperature of 4C. With further increase in
temperature beyond 4C, water then expands.
B. contracts.
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41. Expansion of Water CHECK YOUR NEIGHBOR
When a sample of 4C water is cooled, it
expands.
contracts.
remains unchanged.
There is not enough information.
Explain your answer to your neighbor.
A. expands.
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42. Expansion of Water CHECK YOUR ANSWER
When a sample of 4C water is cooled, it
expands.
contracts.
remains unchanged.
There is not enough information.
Explanation:
Parts of the water will crystallize and occupy more
space.
A. expands.
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43. Heat Transfer Processes of thermal energy transfer: Conduction
Convection
Radiation
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44. Heat Transfer: Conduction
Conduction occurs predominately in solids where the molecules remain in relatively restricted locations.
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45. Heat Transfer: Conduction
Example:
When one end of a solid is placed near a heat source, electrons and adjacent molecules gain kinetic energy and start to move faster and farther. They collide with neighboring molecules and transfer some of their kinetic energy to them. These molecules then interact with other neighboring molecules, and thermal energy is gradually transferred along the solid.
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46. Heat Transfer: Conduction
Good conductors
are composed of atoms with "loose" outer electrons.
are known as poor insulators.
Examples: all metals to varying degrees.
Poor conductors
delay the transfer of heat.
are known as good insulators.
Examples: wood, wool, straw, paper, cork, Styrofoam, liquid, gases, air or materials with trapped air
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47. Heat Transfer: Conduction
No insulator can totally prevent heat from getting through it.
An insulator reduces the rate at which heat penetrates.
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48. Heat Transfer: Conduction CHECK YOUR NEIGHBOR
If you hold one end of a metal bar against a piece of ice, the
end in your hand will soon become cold. Does cold flow from
the ice to your hand?
Yes
In some cases, yes No
In some cases, no
Explain your answer to your neighbor.
C. No.
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49. Heat Transfer: Conduction CHECK YOUR ANSWER
If you hold one end of a metal bar against a piece of ice, the
end in your hand will soon become cold. Does cold flow from
the ice to your hand?
Yes
In some cases, yes No
In some cases, no
Explanation:
Cold does not flow from the ice to your hand. Heat flows from
your hand to the ice. The metal is cold to your touch because
you are transferring heat to the metal.
C. No.
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50. Heat Transfer: Convection
occurs in liquids and gases.
involves the movement of warmer gases or liquids to cooler surroundings.
Two characteristics of convection:
The ability of flow—carrying thermal energy with the fluid
The ability of warm fluid to rise in cooler surroundings
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51. Heat Transfer: Convection CHECK YOUR NEIGHBOR
Although warm air rises, why are mountaintops cold and
snow covered, while the valleys below are relatively warm
and green?
Warm air cools when it rises.
There is a thick insulating blanket of air above valleys.
Both of the above
None of the above
Explain your answer to your neighbor.
C. Both of the above.
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52. Heat Transfer: Convection CHECK YOUR ANSWER
Although warm air rises, why are mountaintops cold and
snow covered, while the valleys below are relatively warm
and green?
Warm air cools when it rises.
There is a thick insulating blanket of air above valleys.
Both of the above.
None of the above.
Explanation:
Earth's atmosphere acts like a blanket, which keeps Earth
from freezing at nighttime.
C. Both of the above.
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53. Heat Transfer: Radiation
Radiation is the process by which thermal energy is transferred by electromagnetic waves.
A thermal energy source such as the Sun converts some of its energy into electromagnetic waves. These waves carry energy, which converts back into thermal energy when absorbed by a receiver. The energy source radiates energy, and a receiver absorbs it.
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54. Heat Transfer: Radiation
The wavelength of radiation is related to the frequency of vibration.
Low-frequency vibrations  long waves
High-frequency vibrations  short waves
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55. Emission of Radiant Energy
All substances at any temperature above absolute zero emit radiant energy.
The average frequency ( ) of radiant energy is directly proportional to the absolute temperature T of the emitter:
 T
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56. Emission of Radiant Energy CHECK YOUR NEIGHBOR
If a good absorber of radiant energy were a poor emitter, its
temperature compared with its surroundings would be
lower.
higher.
unaffected.
none of the above
Explain your answer to your neighbor.
B. higher.
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57. Emission of Radiant Energy CHECK YOUR ANSWER
If a good absorber of radiant energy were a poor emitter, its
temperature compared with its surroundings would be
lower.
higher.
unaffected.
none of the above
Explanation:
If a good absorber were not also a good emitter, there would
be a net absorption of radiant energy, and the temperature of a
good absorber would remain higher than the temperature of
the surroundings. Nature is not so!
B. higher.
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58. Absorption of Radiant Energy
A material's ability to absorb and radiate thermal energy is indicated by its color.
Good absorbers and good emitters are dark in color.
Poor absorbers and poor emitters are reflective or light in color.
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59. Absorption of Radiant Energy
The surface of any material both absorbs and emits radiant energy.
When a surface absorbs more energy than it emits, it is a net absorber, and temperature rises.
When a surface emits more energy than it absorbs, it is a net emitter, and temperature falls.
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60. Absorption of Radiant Energy
Whether a surface is a net absorber or a net emitter depends on whether its temperature is above or below that of its surroundings.
A surface hotter than its surroundings is a net emitter and will cool.
A surface colder than its surroundings is a net absorber and will warm.
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61. Absorption of Radiant Energy CHECK YOUR NEIGHBOR
Which melts faster in sunshine: dirty snow or clean
snow?
Dirty snow
Clean snow
Both of the above
None of the above
Explain your answer to your neighbor.
A. Dirty snow.
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62. Absorption of Radiant Energy CHECK YOUR ANSWER
Which melts faster in sunshine: dirty snow or clean
snow?
Dirty snow
Clean snow
Both of the above
None of the above
Explanation:
Dirty snow absorbs more sunlight, whereas clean
snow reflects more.
A. Dirty snow.
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