PHYS 1010 Exam 2 Study Guide
When a substance absorbs or gives off heat, the internal energy of the substance
Increases or decreases
A good absorber of radiants energy reflects very ________ radiant energy, including visible light
Little
Low-temperature objects radiate ______ wavelengths
Long
Temperature
Measure of the average translational kinetic energy per molecule of a substance
Radiation
energy transmitted by electromagnetic waves
Terrestrial radiation
the radiant energy emitted by Earth
True or false: evaporation and condensation are similar processes
False
True or false: Temperature is a measure of the total kinetic energy in a substance
False
Solar Constant
1400 J/m2 received from the Sun each second at the top of Earth's atmosphere on an area perpendicular to the Sun's rays; expressed in terms of power, 1.4 kW/m2.
What was the precise temperature at the bottom of Lake Michigan, where the water is deep and the winters long, on New Year's Even in 1901?
4C because the temperature at the bottom of any body of water containing any 4C water has a bottom temperature of 4C, for the same reason that rocks are at the bottom
A region of expanding air tends to A. Cool B. Warm C. Both of these D. None of these
A
When Nellie touches a piece of ice with her finger, energy flows A. From her finger to the ice B. From the ice to her finger C. Both of these D. None of these
A
When physicists discuss kinetic energy per molecule, the concept being discussed is A. Temperature B. Heat C. Thermal energy D. Entropy
A
Which of these electromagnetic waves has the lowest frequency? A. Infrared B. Visible C. Ultraviolet D. Gamma rays
A
If a fast marble hits a random scatter of slow marbles, does the fast marble usually speed up or slow down? Of the initially fast-moving marble and the initially slow ones, which lose(s) kinetic energy and which gain(s) kinetic energy? How do these questions relate to the direction of heat flow?
A fast-moving marble slows when it hits slower-moving marbles. It transfers some of its kinetic energy to the slower ones. Likewise with the flow of heat. Molecules with more kinetic energy that are in contact with molecules that have less kinetic energy transfer some of their excess energy to the less energetic ones. The direction of energy transfer is from hot to cold. For both the marbles and the molecules, however, the total energy before and after contact is the same.
Convention
A means of heat transfer by movement of the heated substance itself, such as by currents in a fluid
How is its speed affected when it collides with a receding molecule?
A molecule's speed decreases when colliding with a receding molecule
Wood is a better insulator than glass. Then why is fiberglass commonly used to insulate buildings?
Air is a good insulator. Fiberglass is a good insulator because of the air that's trapped among its fibers
Thermal expansion
An increase in the size of a substance when the temperature is increased
Does a good insulator prevent or merely slow the transfer of thermal heat?
An insulator slows heat transfer
All matter - solid, liquid, gas and plasma, is comprised of
Atoms or molecules
A given material that is quick to heat up has a A. High specific heat capacity B. Low specific heat capacity C. High or low specific heat capacity D. None of the above
B
Before ice forms on a lake, all the water in the lake must be cooled to A. 0C B. 4C C. A value slightly below 0C D. None of these
B
In practice, a good insulator A. Stops heat flow B. Slows heat flow C. Speeds negative heat flow D. All of the above
B
San Fransisco has milder winters than Washington D.C. because of water's high A. Conductivity B. Specific heat capacity C. Temperature in the Pacific Ocean D. None of the above
B
The pupils of your eyes A. Are black and therefore are net absorbers of light B. Are net absorbers of light and therefore appear black C. Block light from within from emerging D. All of the above
B
Thermal convection is linked mostly to A. Radiant energy B. Fluids C. Insulators D. All of these
B
Why can you place your hand briefly inside a hot oven without harm?
Because air is a poor conductor of heat
True or false: Air is a good conductor
False
A friend says that because tar paper is black, it therefore absorbs light. Another friend says that tar paper absorbs light and is therefore black. Which statement do you prefer?
Both statements are correct
In the absence of wind, why does warmed air rise vertically?
Buoyancy acts counter to gravity, upward
A bimetallic strip used in thermostats relies on the fact that different metals have different A. Specific heat capacities B. Thermal energies at different temperatures C. Rates of thermal expansion D. All of these
C
Glass in a florist's greenhouse acts as a one-way valve in that it A. Let's light energy flow only in one direction B. Cuts off unwanted radiation C. Allows high-frequency waves in and blocks low-frequency waves from exiting D. Is transparent only to lower-frequency waves
C
Heat is thermal energy that flows due to A. Molecular speed B. Calorie imbalance C. Temperature differences D. None of the above
C
Molecules in a constant-temperature mixture of gases have the same average A. Speed B. Velocity C. Kinetic energy D. All of the above
C
Water at 4C will expand when it is slightly A. Cooled B. Warmed C. Both of these D. None of these
C
White-hot sparks from a fireworks sparkler are harmless when striking your skin because A. They have a low temperature B. The energy per molecule is very low C. The energy per molecule is high, but the total energy transferred is small D. All of the above
C
What are two ways heat can be measured in?
Calorie or joules
Boiling
Change from liquid to gas occurring beneath the surface of the liquid
When temperature is decreased, nearly all materials tend to
Contract
A water-filled paper cup held in a flame will not catch fire because A. The inside of the paper is wet B. Water is an excellent conductor of heat C. Paper is a poor conductor of heat D. The paper cup cannot become appreciably hotter than the water it contains
D
Compared with terrestrial radiation, the radiation from the Sun has A. A longer wavelength B. A lower frequency C. Both a longer wavelength and a lower frequency D. Neither a longer wavelength nor a lower frequency
D
Every equation in physics reminds us of a lesson: We can never change only one thing. When we change the composition of the atmosphere we likely also change A. Its transparency B. Its reflectivity C. Earth's climate D. All of the above
D
To save energy while you leave your warm house for several hours on a cold day, turn the thermostat A. Down B. Up C. To room temperature D. Off
D
Heat is _________ is transit from a body of higher temperature to one of lower temperature
Energy
Solar power
Energy per unit time received from the Sun.
In winter, why does the road surface on a bridge tend to be more icy than the road surfaces at either end of the bridge?
Energy radiated by roads on land is partly replenished by head conducted from the warmer ground below the pavement. But there's no thermal contact between the road surfaces of bridges and the ground, so they receive very little replenishing energy conducted from the ground
When temperature is increased, nearly all materials tend to
Expand
To repair a dented ping-pong ball, why is it a good idea to place it in boiling water?
Expansion of air inside the ping-pong ball will likely pop it back to its original shape
Why do both a party balloon and a railroad track increase in size when their temperature rise?
Heated molecules in each jiggle faster and occupy more space, much more for the balloon because it is gaseous
You can hold your fingers beside the candle flame without harm, but not above the flame. Why?
Hot air travels upward by air convection. Since air is a poor conductor, very little heat travels sideways to your fingers.
Specific Heat Capacity
How much heat is required to raise the temperature of a unit mass of a substance by 1 degree Celsius
If a good absorber of radiant energy were a poor emitter, how would its temperature compare with the temperature of its surroundings?
If a good absorber were not also a good emitter, there would be a net absorption of radiant energy and the temperature of the absorber would remain higher than the temperature of the surroundings. Things around us approach a common temperature only because good absorbers are, by their very nature, also good emitters.
What is meant by the statement, "you can never change only one thing?"
If you change a variable on one side of an equation, a variable on one side of an equation, a variable on the other side has to change
If poisons are placed in a landfill, we alter the composition of the land. If a few milliliters of chlorine are put in a swimming pool, we alter the water in the pool. How can billions of tons of greenhouse gases be discharged into the atmosphere without altering its composition?
It can't
Which is likely to be colder: a night when you can see the stars or a night when you cannot?
It is colder on the starry night, when Earth's surface radiates directly to frigid deep space. On a cloudy night, net radiation is less because the clouds radiate energy back to Earth's surface.
Does a substance with a low specific heat capacity warm quickly or slowly when heat is applied?
It warms quickly. Low specific heat capacity means a quicker change in temperature
Why is ice slippery?
Its crystalline structure is not easily maintained at the surface
Suppose you apply a flame to 1L of water for a certain time and its temperature rises by 2C. If you apply the same flame for the same time to 2L of water, by how much will its temperature rise?
Its temperature will rise by only 1C because there are twice as many molecules in 2L of water, and each molecule receives only half as much energy on average
Because of the random motion of matter, the atoms and molecules in matter have what type of energy?
Kinetic
Why do you get burned if you touch the metal sides of the oven?
Metal overall is an excellent conductor of heat
Which raises the water temperature more: the addition of 1 calorie or 4.19 J?
Neither. They expressed the same amount of energy in different units
Since a hot cup of tea loses heat more rapidly than a lukewarm cup of tea, is it correct to say that a hot cup of tea will cool to room temperature before a lukewarm cup of tea will?
No! Although the rate of cooling is greater for the hotter cup, it has farther to cool to reach thermal equilibrium.
If the water level in a dish of water remains unchanged from one day to the next, can you conclude that no evaporation or condensation has occurred?
No, because a lot of activity it taking place at the molecular level. Both evaporation and condensation occur continuously
Would evaporation be a cooling process if molecules of every speed had an equal chance to escape from the liquid surface?
No. If molecules of all speeds escaped equally easily from the surface, the molecules left behind would have the same range of speeds as before any escaped, and there would be no change in the liquid's temperature. When only the faster molecules can break free, those that remain are slower and the liquid becomes cooler.
Equation for Newton's Law of Cooling
Rate of cooling ~ ΔT
High-temperature objects radiate ______ wavelengths
Short
Why do fish benefit from water being most dense at 4C?
Since water is most dense at 4C, colder water rises and freezes on the surface, making the fish survive in relative warmth
What eventually happens to the solar energy that falls on Earth?
Sooner or later, it will be radiated back into space. Energy is always in transit—you can rent it, but you can't own it.
Evaporation
The change of phase from liquid to gas that takes place at the surface of a liquid
Condensation
The change of phase of a gas into a liquid
Conduction
The direct transfer of heat from one substance to another substance that it is touching.
Heat
The energy that "flows" from one object to another by virtue of a difference in temperature
An iron tack and a big iron bolt, both red-hot at the same temperatures, are dropped into identical contains of same-temperature water. Which one raise the water temperature more?
The iron bolt, having more internal energy at the same temperature of the smaller tack, raises the temperature of water more.
How is the speed of an air molecule affected when hit by an approaching faster-moving molecule?
The molecule being hit rebounds with increased speed
Newton's Law of Cooling
The rate of cooling of an object is approximately proportional to the temperature difference between the object and its surroundings
What is the ultimate source of all the world's energy (excluding nuclear energy)?
The sun
Internal energy
The total energy stored in the atoms and molecules within a substance
Internal Energy
The total of all molecular energies, kinetic plus potential, that are internal to a substance.
Convection
The transfer of heat energy in a gas or liquid by means of currents in the heated fluid. The fluid moves, carrying energy with it.
A farmer turns on the propane burner in his barn on a cold morning and heats the air to 68F. Why does he still feel cold?
The walls of the barn are still cold. The farmer radiates more energy to the walls than the walls radiate back, and he is chilled
We can think of specific heat capacity as what?
Thermal inertia
Changes in internal energy are of principal concern in
Thermodynamics
What is an example of conduction?
Touching a hot pan
What does it mean to say that the greenhouse effect is like a one-way valve?
Transparent material—atmosphere for Earth and glass for the greenhouse— allows only incoming short wavelengths and blocks outgoing long wavelengths. As a result, radiant energy is trapped within the "greenhouse."
True or false: Air is a good insulator
True
True or false: Matter does not contain heat
True
True or false: The feeling of warmth or cold for different materials involves rates of heat transfer, not necessarily temperatures
True
Convection currents are produced by _________ heating of land and water
Uneven
Why is a packed of warmed air less dense than a same-mass packet of cooler air?
Warmed air is less dense because faster-moving molecules occupy more space than the slower-moving molecules of cooler air
Greenhouse Effect
Warming caused by short-wavelength radiant energy from the Sun that easily enters the atmosphere and is absorbed by Earth, but when radiated at longer wavelengths cannot easily escape Earth's atmosphere
Which has a higher specific heat capacity: water or sand?
Water
Why does a piece of watermelon stay cool for a long time than sandwiches when both are removed from a picnic cooler on a hot day?
Water in the watermelon has more "thermal inertia" than sandwich ingredients, and it resists changes in temperature much more.
Why does dew form on the surface of a cold soft-drink can?
Water vapor in the warm air is chilled when it makes contact with the cold can
Absolute zero
When a substance has absolutely no kinetic energy to give up
Why do molecules decrease in size when they cool?
When molecules are cooled off, they jiggle slower and settle into less space
When does convection occur?
Wherever fluids are subjected to temperature differences
Does evaporation occur beneath the surface of water as it boils?
Yes'm as evidenced by the bubbles that form
What are the three methods of heat transfer?
conduction, convection, radiation
Equation for specific heat capacity
q = mcΔT