University Physics Volume 2

# Conceptual Questions

University Physics Volume 2Conceptual Questions

### 4.1Reversible and Irreversible Processes

1.

State an example of a process that occurs in nature that is as close to reversible as it can be.

### 4.2Heat Engines

2.

Explain in practical terms why efficiency is defined as $W/Qh.W/Qh.$

### 4.3Refrigerators and Heat Pumps

3.

If the refrigerator door is left open, what happens to the temperature of the kitchen?

4.

Is it possible for the efficiency of a reversible engine to be greater than 1.0? Is it possible for the coefficient of performance of a reversible refrigerator to be less than 1.0?

### 4.4Statements of the Second Law of Thermodynamics

5.

In the text, we showed that if the Clausius statement is false, the Kelvin statement must also be false. Now show the reverse, such that if the Kelvin statement is false, it follows that the Clausius statement is false.

6.

Why don’t we operate ocean liners by extracting heat from the ocean or operate airplanes by extracting heat from the atmosphere?

7.

Discuss the practical advantages and disadvantages of heat pumps and electric heating.

8.

The energy output of a heat pump is greater than the energy used to operate the pump. Why doesn’t this statement violate the first law of thermodynamics?

9.

Speculate as to why nuclear power plants are less efficient than fossil-fuel plants based on temperature arguments.

10.

An ideal gas goes from state $(pi,Vi)(pi,Vi)$ to state $(pf,Vf)(pf,Vf)$ when it is allowed to expand freely. Is it possible to represent the actual process on a pV diagram? Explain.

### 4.5The Carnot Cycle

11.

To increase the efficiency of a Carnot engine, should the temperature of the hot reservoir be raised or lowered? What about the cold reservoir?

12.

How could you design a Carnot engine with $100%100%$ efficiency?

13.

What type of processes occur in a Carnot cycle?

### 4.6Entropy

14.

Does the entropy increase for a Carnot engine for each cycle?

15.

Is it possible for a system to have an entropy change if it neither absorbs nor emits heat during a reversible transition? What happens if the process is irreversible?

### 4.7Entropy on a Microscopic Scale

16.

Are the entropy changes of the systems in the following processes positive or negative? (a) water vapor that condenses on a cold surface; (b) gas in a container that leaks into the surrounding atmosphere; (c) an ice cube that melts in a glass of lukewarm water; (d) the lukewarm water of part (c); (e) a real heat engine performing a cycle; (f) food cooled in a refrigerator.

17.

Discuss the entropy changes in the systems of Question 21.10 in terms of disorder.