Question 1

Which statement best describes the second law of thermodynamics (Kelvin–Planck statement)?

Accepted Answer

It is impossible for any system to undergo a process in which it absorbs heat from a reservoir at a single temperature and converts the heat completely into mechanical work, with the system ending in the same state in which it began.

Question 2

A heat engine absorbs $$Q_H = 10,000\ J$$ from a hot reservoir and delivers $$W = 2,000\ J of $$mechanical work per cycle. What is the thermal efficiency $$e of $$this engine?

Accepted Answer

$$e = \frac{W}{Q_H} = \frac{2,000\ J}{10,000\ J} = 0.20 = 20\%$$

Question 3

In a four-stroke internal-combustion engine (Otto cycle), which stroke corresponds to the adiabatic expansion?

Accepted Answer

Power stroke

Question 4

Which equation correctly expresses the thermal efficiency $$e of a $$heat engine?

Accepted Answer

$$e = \frac{W}{Q_H}$$

Question 5

A refrigerator removes heat $$Q_C$$ from its interior and requires mechanical work $$W. $$What is the coefficient of performance $$K$$?

Accepted Answer

$$K = \frac{Q_C}{W}$$

Question 6

Which process in the Carnot cycle is responsible for absorbing heat from the hot reservoir?

Accepted Answer

Isothermal expansion at $$T_H$$

Question 7

What is the maximum possible efficiency of a heat engine operating between two temperatures $$T_H$$ and $$T_C$$?

Accepted Answer

$$e = 1 - \frac{T_C}{T_H}$$

Question 8

Which statement about entropy is correct?

Accepted Answer

Entropy is a quantitative measure of randomness or disorder.

Question 9

During an isothermal reversible process, the change in entropy $$\Delta S is $$given by:

Accepted Answer

$$\Delta S = \frac{Q}{T}$$

Question 10

A gasoline engine burns 0.20 g of gasoline per cycle and operates at 25 cycles per second. What is the mass of gasoline burned per hour?

Accepted Answer

$$18\ kg$$

Question 11

Which of the following is true for a reversible adiabatic process?

Accepted Answer

The entropy change $$\Delta S is $$zero.

Question 12

Which statement about the Otto cycle efficiency is correct?

Accepted Answer

Efficiency increases as the compression ratio $$r$$ increases.

Question 13

Which equation represents the thermal efficiency of the Otto cycle?

Accepted Answer

$$e = 1 - \frac{1}{r$$^{\gamma - 1}$$}$$

Question 14

Which statement about the Diesel cycle is correct?

Accepted Answer

The compression ratio $$r$$ can be much higher than for a gasoline engine because there is no fuel in the cylinder during the compression stroke.

Question 15

Which of the following is a correct statement of the Clausius form of the second law of thermodynamics?

Accepted Answer

It is impossible for any process to have as its sole result the transfer of heat from a cooler to a hotter object.

Question 16

Which of the following best describes why thermodynamic processes in nature are irreversible?

Accepted Answer

Irreversible processes proceed naturally in the direction of increasing entropy.

Question 17

If you leave the refrigerator door open in your house, what happens to the temperature of the house?

Accepted Answer

The house will get warmer because the refrigerator releases more heat to the room than it removes from inside.

Question 18

Which equation gives the entropy $$S of a $$macroscopic state in terms of the number of microscopic states $$w$$?

Accepted Answer

$$S = k_B \ln w$$

Question 19

Which statement about the Carnot engine is correct?

Accepted Answer

No engine can be more efficient than a Carnot engine operating between the same two temperatures.

Question 20

In a reversible cyclic process, what is the total entropy change?

Accepted Answer

Zero

The Second Law of Thermodynamics: Heat Engines, Refrigerators, and Entropy

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