Physics Ch. 16 Questions

"Heat Transfer" Reading Check and HW
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What is the role of "loose" electrons in heat conductors?
Free electrons can move through a material carrying heat, jostling atoms and other electrons.
If you touch the metal sides in an oven with your bare hand, you're in trouble. But hold your hand briefly in the oven air and you're okay. What does this tell you about the relative conductivities of metal and air?
Metal is a good conductor of heat, whereas air is a terrible conductor of heat.
Explain why a firewalker can step quickly without harm on red-hot coals with bare feet.
Wood, even as glowing coals, is a poor conductor of heat.
Why are materials such as wood, fur, feathers, and even snow good insulators?
Outer electrons in these materials are firmly attached.
Does a good insulator prevent heat from escaping or slow its passage?
Insulators slow the passage of heat.
*well-insulated house; prevents heat from escaping
NOT blocking cold from entering
What happens to the volume of air as it rises? What happens to its temperature?
Volume increases;
temperature decreases.
*releasing a 1/2 filled balloon from ground; expands as it rises in atmosphere
When an air molecule is hit by an approaching, faster moving molecule, does the approaching molecule's rebound speed increase or decrease? How about when it hits a receding molecule?
increase, decrease
*approaching molecule will rebound with increased speed; rebound with decreased speed with a receding molecule
How are the speeds of molecules of air affected when the air is compressed by the action of a tire pump? What happens to the temperature of the air?
Speeds increase; temperature increases.
How are the speeds of molecules of air affected as they separate from one another when escaping from the nozzle of a party balloon? What happens to the temperature of the air?
Speeds decrease; temperature decreases.
Why isn't Millie's hand burned when she holds it above the escape valve of the pressure cooker (see Figure 16.8 in the textbook)?
The escaping gas is cooled by expansion.
Why does the direction of coastal winds change from day to night?
The specific heat of water is greater than the specific heat of land. Water cools more slowly at night. The temperature difference drives convection and offshore winds.
In what form does radiant energy travel?
As electromagnetic waves
Relatively speaking, do high-frequency waves have long wavelengths or short wavelengths? Name an electromagnetic wave with higher frequency than blue light.
Short, ultraviolet
How does the peak frequency of radiant energy relate to the absolute temperature of the radiating source?
The peak frequency increases as temperature increases.
What is terrestrial radiation?
Terrestrial radiation is infrared radiation emitted by Earth's surface.
Cite a primary difference between waves of solar radiation and waves of terrestrial radiation.
Solar radiation peaks at shorter wavelengths in the visible, whereas terrestrial radiation peaks at longer wavelengths in the infrared.
Since all objects emit energy to their surroundings, why don't the temperatures of all objects continuously decrease?
Objects that are good emitters are equally good absorbers, so they absorb radiation as well as emit it.
What determines whether an object is a net absorber or a net emitter of radiant energy at a given time?
It is determined by the temperature of the object relative to its surroundings. Hotter objects are net emitters.
Which will normally warm faster: a black pot of cold water or a silvered pot of cold water? Which will cool faster?
Black, black
Can an object be both a good absorber and a good reflector at the same time?
No. A good absorber reflects very little light.
Why does the pupil of the eye appear black?
Light that enters the pupil bounces several times before exiting, and is absorbed on each bounce, so little light exits.
What happens to the temperature of something that radiates energy without absorbing the same amount in return?
It cools.
An object that radiates energy at night is in contact with the relatively warm Earth. How does poor conductivity affect the object's temperature relative to the air temperature?
Poor thermal conductivity causes it to get colder with respect to the air than good thermal conductivity does.
Which will undergo the greater rate of cooling: a red-hot poker in a warm oven or a red-hot poker in a cold room (or do both cool at the same rate)?
The poker in the cold room cools fastest.
What does a windchill of -20°C mean?
The cooling rate will be the same as if the temperature were -20°C without wind.
What would be the consequence of completely eliminating the greenhouse effect?
The average temperature on the surface of Earth would drop to -18°C.
How does glass act like a one-way valve for a conventional greenhouse? Does the atmosphere similarly act as a one-way valve?
Glass transmits solar radiation into the greenhouse and blocks infrared radiation from leaving the greenhouse. The same thing happens in the atmosphere.
Distinguish between weather and climate.
Climate is what you expect, whereas weather is what you get.
How much radiant energy from the Sun, on average, reaches each square meter at the top of Earth's atmosphere each second? What is the average solar power, averaged over a whole year, which reaches the United States?
1.4 kJ, 0.18 kW/m2
Cite three ways in which a Thermos bottle inhibits heat transfer.
There is no conduction and no convection through a vacuum, and silvered surfaces stops radiation.
Suppose that, at a restaurant, you are served coffee before you are ready to drink it. In order that it be hottest when you are ready for it, should you add cream to the coffee right away or wait until you are ready to drink it?
by adding the cream right away, you are increasing the volume of liquid in the cup; a larger sample will cool down more slowly. Also, since the very hot coffee would also cool quickly, adding cream will lower the temperature and heat loss of the coffee.
At what common temperature will a block of wood and a block of metal both feel neither hot nor cold to the touch?
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If you hold one end of a piece of metal against a piece of ice, the end in your hand soon becomes cold. Does cold flow from the ice to your hand? Explain.
the heat from your hand flows into the ice via the metal, quite efficiently, as metal is a very good conductor.
Is it possible for heat to flow between two objects with the same internal energy? Can heat flow from an object with less internal energy to one with more internal energy? Defend your answers.
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Why is it incorrect to say that, when a hot object warms a cold one, the increase in temperature of the cold one is equal to the decrease in temperature of the hot one? When is this statement correct?
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Ceiling fans can make you feel cooler in a warm room. Do ceiling fans reduce room temperature?
convection