Physics Chapter 14
What is the emissivity of a perfect reflector?
0 (no units) Reason: Since a perfect reflector cannot emit or absorb radiation, and the minimum value of the emissivity is 0 (no units), the emissivity of a perfect reflector is 0 (no units).
Rank the following objects according to their heat capacity, with the largest heat capacity at the top and the smallest at the bottom.
1 k 2 k 100 k 1000 k
According to the equipartition of energy theorem, how much energy is given to each independent mode of storage on average?
1/2kT
Rank the following substances according to their specific heat, with the largest specific heat at the top and the smallest at the bottom.
100 j 1 k 50 j 1 k 1000 j 10 k 400 j 20 k
Rank the following amounts of energy, with the largest amount of energy at the top and the smallest at the bottom.
12 calorie 3 calorie 4 joule
The initial temperatures of objects A, B, and C are TA = 250 K, TB = 260 K, and TC = 350 K. They are then placed in thermal contact with each other. Select all of the following that could be the final equilibrium temperature of them. Assume no phase changes.
260 K 300 K
Four pieces of wood used to construct a house are identical except for their temperatures and elevations above the ground. Rank the pieces of wood according to their internal energies, with the largest internal energy at the top and the smallest at the bottom.
300 0 273 30 255 20 225 10
If equal amounts of water at 5°C and 95°C are mixed, then what will be the final temperature?
50°C
The electromagnetic radiation emitted by a distant star is measured by an astronomer. She determines that the wavelength of maximum radiation for the star is 500 nm. What is the approximate surface temperature of the star?
6000 K
What minimum mass of water at 100°C is required to completely melt 1 kg of ice at 0°C?
800 g Reason: (1 kg)(333.7 kJ/kg) = (mwater)(419 kJ/kg), so (333.7 kJ)/(419 kJ/kg) = 0.8 kg = 800 g
According to Stefan's radiation law, match the relationship in the left column with the proportionality in the right column.
A and P directly P and o not proportional T and P proportional but not directly
What is a supercritical fluid?
A fluid that is both above the critical temperature and above the critical pressure
Select all of the quantities below that are not equal to zero for the individual random motions of molecules.
Average rotational kinetic energy Average translational kinetic energy
If equal masses of ice at 0°C and water at 80°C are mixed, then what will be the final temperature of the mixture?
Between 0°C and 40°C Reason: mc(80°C - Tf) = mLf, ice + mc(Tf - 0°C); since m and c are equal, then Tf is closer to 0°C than to 80°C.
If equal masses of ice at 0°C and steam at 100°C are mixed, then what will be the final temperature of the mixture?
Between 50°C and 100°C
If water of mass m at 5°C and water of mass 2m at 95°C are mixed, then what will be the final temperature?
Between 50°C and 95°C
Four rectangular solid blocks of differing thicknesses are placed side by side. The blocks on the ends are kept at different temperatures so that heat flows across all of them. Each block is made of the same material and has the same cross-sectional area. Rank the blocks according to the temperature difference across them, with the largest temperature difference at the top and the smallest at the bottom.
C is 5 cm D 10 mm A 5mm D 2500 um
Which of the following can be considered "Greenhouse gases"?
CO2 Water vapor
Match the following molar specific heats at constant volume.
Cv = (3/2)R Choice, Molar specific heat at constant volume for a monatomic ideal gas Molar specific heat at constant volume for a monatomic ideal gas Cv = (5/2)R Choice, Molar specific heat at constant volume for a diatomic ideal gas Molar specific heat at constant volume for a diatomic ideal gas
Which of the following is the molar specific heat at constant volume for a monatomic ideal gas?
Cv = 3/2R
Select all of the following objects within which thermal conduction can occur.
Earth's atmosphere Tea kettle hotter on the bottom and cooler at the top Pacific Ocean warmer at the surface and cooler below
Select all of the following that are true regarding evaporation.
Evaporation is a cooling process. The rate of evaporation of water molecules into air decreases as the humidity of the air increases.
True or false: The calorie used in physics and the Calorie used in measuring the energy content of food are the same.
False
True or false: When heat flows into the system, Q < 0.
False
Which statement is correct?
Heat and temperature are related.
What is the ratio of heat to the temperature change of a system?
Heat capacity
What is the specific heat of a substance?
Heat capacity per unit mass
Select all of the following statements that are true.
Heat is a form of energy. Heat flows from one object to another due to a temperature difference between the objects.
What is the graph of temperature versus heat for a latent heat process?
Horizontal line
Select all of the following situations in which heat would flow.
Ice cubes at 0°C are placed in a glass of water at 20°C. A tea kettle made of copper at 300 K is placed on top of a campfire at 800 K.
Select all the independent ways a diatomic molecule can store energy at room temperature.
In translational kinetic energy along three independent directions In rotational kinetic energy about two independent axes.
Select all of the following that help explain why most objects expand when their temperatures increase.
Interatomic and intermolecular forces are highly asymmetrical. Atoms and molecules vibrate about their equilibrium positions, even in a solid.
Select all of the following in which heat would flow spontaneously from object B to object A.
Internal energyA = 200 kJ, TA = 400 K, internal energyB = 800 kJ, TB = 700 K Internal energyA = 300 kJ, TA = 100 K, internal energyB = 200 kJ, TB = 900 K
What are some of the ways that Earth's atmosphere helps to keep the surface warm?
It absorbs much of the longer-wavelength IR and reemits half back to Earth's surface. It allows much of the short wavelength IR from the Sun through to Earth's surface.
What is the net effect of global convection?
It moves thermal energy from warmer areas to cooler areas.
Select all of the following that are valid units for specific heat.
J/(K⋅g) J/(K⋅kg)
Select all of the following that are valid units for heat capacity.
J/K J/(degree C)
Select all of the following that are due to the fact that the slope of the fusion curve is negative on the phase diagram of water.
Liquid water expands when it freezes. Ice is less dense than liquid water.
In which phases of matter can thermal convection occur?
Liquids and gases only
What is the net heat flow due to thermal radiation between an object and its environment if the environment is at a higher temperature than the object?
Negative
Unequal masses of identical substances are brought into thermal contact while being insulated from the environment. Object A is initially at 20°C, and object B is initially at 80°C. If the final temperature of the mixture is 70°C, then how are the masses of the objects related?
Object A has a less mass than object B. Reason: mAcA(Tf - 20°C) = mBcB(80°C - Tf); since cA = cB and Tf = 70°C, then mA < mB.
Select all of the following bodies within which natural thermal convection can occur.
Pacific Ocean warmer at the surface and cooler below Earth's atmosphere
What changes on the microscopic level during a phase change? Assume that there is no temperature change.
Potential energy
What changes on the microscopic level during a phase change? Assume that there is no temperature change.
Potential energy Reason: The kinetic energy of the molecules is not changing, but their potential energy is changing.
Initially, the temperature of the system is 50 K and the temperature of the environment is 80 K. Later, the temperatures of the system and environment are the same. Which statement is true?
Q > 0
The initial temperatures of objects A, B, and C are TA = 250 K, TB = 260 K, and TC = 350 K. They are then placed in thermal contact with each other. Select all of the following that could represent the heat flowing into or out of them. Assume no phase changes.
QA > 0, QB > 0, QC < 0 QA > 0, QB < 0, QC < 0
What can determine part of the internal energy of a system?
Random motion of its molecules
Which phases of matter can emit thermal radiation?
Solids, liquids, and gases
Within which phases of matter can thermal conduction occur?
Solids, liquids, and gases
Select all of the following that are true regarding monatomic ideal gases.
Some examples of monatomic ideal gases are helium and neon. They are gases in which atoms are not bound to other atoms. The internal energy includes translational kinetic energy.
Which of the following contribute to convection?
Storms in the atmosphere The currents in the oceans
Equal masses of substance A and B are brought into thermal contact while being insulated from the environment. Substance A is initially at 20°C, and substance B is initially at 80°C. If the final temperature of the mixture is 70°C, then how are the specific heats of the substances related?
Substance A has a smaller specific heat than substance B.
Select all of the following statements that are true.
Systems possess neither heat nor work. Heat and work are both kinds of energy transfer.
What does the flow of heat tend to equalize?
Temperature
Select all of the following that are included in a phase diagram.
Temperature State of matter Pressure
Select all of the following processes that can occur in monatomic ideal gases.
Temperature decrease Temperature increase
Select all of the following processes that can occur in diatomic ideal gases.
Temperature increase Temperature decrease
Why doesn't temperature change during a phase transition?
The change in energy during a phase transition is related to potential energy (molecular bonds) rather than kinetic energy (temperature).
Equal mass pieces of lead and ice each absorb the same quantity of heat in a laboratory experiment. The resulting change in temperature of the ice is less than the resulting change in temperature of the lead. Select all of the following that are implied by these measurements.
The heat capacity of lead is less than the heat capacity of ice. The specific heat of lead is less than the specific heat of ice. Reason: Q/m = c ΔT = constant. ΔTice < ΔTlead, so Cice > Clead
Equal mass pieces of lead and ice each absorb the same quantity of heat in a laboratory experiment. The resulting change in temperature of the ice is less than the resulting change in temperature of the lead. Select all of the following that are implied by these measurements.
The heat capacity of lead is less than the heat capacity of ice. The specific heat of lead is less than the specific heat of ice.
How does evaporation cool something?
The highest energy particles escape, carrying energy away with them.
Select all of the following that are true regarding diatomic ideal gases.
The internal energy includes translational kinetic energy. The internal energy includes rotational kinetic energy.
What is the result of solid water (ice) having a lower density than liquid water?
The slope of the fusion curve is negative.
Equal mass pieces of lead and ice each absorb the same quantity of heat in a laboratory experiment. The resulting change in temperature of the ice is less than the resulting change in temperature of the lead. Select all of the following that are implied by these measurements.
The specific heat of lead is less than the specific heat of ice. The heat capacity of lead is less than the heat capacity of ice.
Select all of the following that are true regarding thermal conduction.
Thermal conduction is due to collisions of atoms and molecules. Thermal conduction occurs both within an object and between objects that are in thermal contact.
Five rectangular solid blocks of differing thicknesses are placed side by side. The blocks on the ends are kept at different temperatures so that heat flows across all of them. Each block is made of the same material and has the same cross-sectional area. Select all of the following quantities that are the same for each block.
Thermal conductivity Rate of heat flow
Select all of the following that are true regarding thermal convection.
Thermal convection is due to the net translational motion of atoms and molecules. Thermal convection occurs only within a body.
Select all of the following that are true regarding thermal radiation.
Thermal radiation can be emitted, absorbed, or both. Thermal radiation is electromagnetic.
Select all of the following statements that are true regarding thermal radiation.
Thermal radiation consists of electromagnetic waves. Thermal radiation is created when electrical charges oscillate.
Select all of the following that are true regarding thermal radiation.
Thermal radiation is electromagnetic. Thermal radiation can be emitted, absorbed, or both.
How are the wavelength of maximum radiation and absolute temperature related for a blackbody?
They are inversely proportional.
Select examples of forced convection.
Warm air from a furnace being blown into a room Hot water from a heater being pumped through a radiator Explanation: For forced convection to take place, the motion of cold or hot fluid has to be forced upon.
Select all of the following statements that are true.
Work requires macroscopic displacement whereas heat does not. Heat requires a temperature difference whereas work does not.
What is the net heat flow between an object and its environment if they are at thermal equilibrium?
Zero
Choose the answer that completes the sentence: The average distance between atoms in a solid tends to increase with temperature as the ________ of the atoms increases.
amplitude of vibration
The amounts of heat added to increase the temperature of 1.0 kg samples of copper and aluminum are shown in the graph. What does this imply?
ccopper < caluminum
Which of the following expressions is equal to the thermal resistance in Fourier's law of heat conduction?
d/(κA)
According to Wien's law, as the temperature of an object is increased, the maximum emission of blackbody radiation (peak in the spectrum) will ______.
shift to shorter wavelengths
Rank the following molecules according to their molar specific heat at constant volume, with the largest molar specific heat at constant volume at the top and the smallest at the bottom. Assume that the temperature is sufficiently high.
translational kinetic energy along three axes, rotational kinetic energy about two perpendicular axes translational kinetic energy along two axes, rotational kinetic energy about two perpendicular axes translational kinetic energy along three axes, no rotational kinetic energy translational kinetic energy along one axes, rotational kinetic energy about one perpendicular axes
Which of the following expressions is equal to the temperature gradient in Fourier's law of heat conduction?
ΔT/d
