College Physics

# Conceptual Questions

College PhysicsConceptual Questions

## 13.1Temperature

1.

What does it mean to say that two systems are in thermal equilibrium?

2.

Give an example of a physical property that varies with temperature and describe how it is used to measure temperature.

3.

When a cold alcohol thermometer is placed in a hot liquid, the column of alcohol goes down slightly before going up. Explain why.

4.

If you add boiling water to a cup at room temperature, what would you expect the final equilibrium temperature of the unit to be? You will need to include the surroundings as part of the system. Consider the zeroth law of thermodynamics.

## 13.2Thermal Expansion of Solids and Liquids

5.

Thermal stresses caused by uneven cooling can easily break glass cookware. Explain why Pyrex®, a glass with a small coefficient of linear expansion, is less susceptible.

6.

Water expands significantly when it freezes: a volume increase of about 9% occurs. As a result of this expansion and because of the formation and growth of crystals as water freezes, anywhere from 10% to 30% of biological cells are burst when animal or plant material is frozen. Discuss the implications of this cell damage for the prospect of preserving human bodies by freezing so that they can be thawed at some future date when it is hoped that all diseases are curable.

7.

One method of getting a tight fit, say of a metal peg in a hole in a metal block, is to manufacture the peg slightly larger than the hole. The peg is then inserted when at a different temperature than the block. Should the block be hotter or colder than the peg during insertion? Explain your answer.

8.

Does it really help to run hot water over a tight metal lid on a glass jar before trying to open it? Explain your answer.

9.

Liquids and solids expand with increasing temperature, because the kinetic energy of a body’s atoms and molecules increases. Explain why some materials shrink with increasing temperature.

## 13.3The Ideal Gas Law

10.

Find out the human population of Earth. Is there a mole of people inhabiting Earth? If the average mass of a person is 60 kg, calculate the mass of a mole of people. How does the mass of a mole of people compare with the mass of Earth?

11.

Under what circumstances would you expect a gas to behave significantly differently than predicted by the ideal gas law?

12.

A constant-volume gas thermometer contains a fixed amount of gas. What property of the gas is measured to indicate its temperature?

## 13.4Kinetic Theory: Atomic and Molecular Explanation of Pressure and Temperature

13.

How is momentum related to the pressure exerted by a gas? Explain on the atomic and molecular level, considering the behavior of atoms and molecules.

## 13.5Phase Changes

14.

A pressure cooker contains water and steam in equilibrium at a pressure greater than atmospheric pressure. How does this greater pressure increase cooking speed?

15.

Why does condensation form most rapidly on the coldest object in a room—for example, on a glass of ice water?

16.

What is the vapor pressure of solid carbon dioxide (dry ice) at $–78.5ºC–78.5ºC size 12{ +- "78" "." 5°C} {}$?

Figure 13.35 The phase diagram for carbon dioxide. The axes are nonlinear, and the graph is not to scale. Dry ice is solid carbon dioxide and has a sublimation temperature of $–78.5ºC–78.5ºC size 12{ +- "78" "." 5°C} {}$.
17.

Can carbon dioxide be liquefied at room temperature ($20ºC20ºC size 12{"20"°C} {}$)? If so, how? If not, why not? (See Figure 13.35.)

18.

Oxygen cannot be liquefied at room temperature by placing it under a large enough pressure to force its molecules together. Explain why this is.

19.

What is the distinction between gas and vapor?

## 13.6Humidity, Evaporation, and Boiling

20.

Because humidity depends only on water’s vapor pressure and temperature, are the saturation vapor densities listed in Table 13.5 valid in an atmosphere of helium at a pressure of $1.01×105 N/m21.01×105 N/m2 size 12{1 "." "01"´"10" rSup { size 8{5} } " N/m" rSup { size 8{2} } } {}$, rather than air? Are those values affected by altitude on Earth?

21.

Why does a beaker of $40.0ºC40.0ºC size 12{"40" "." 0°C} {}$ water placed in a vacuum chamber start to boil as the chamber is evacuated (air is pumped out of the chamber)? At what pressure does the boiling begin? Would food cook any faster in such a beaker?

22.

Why does rubbing alcohol evaporate much more rapidly than water at STP (standard temperature and pressure)?

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