Lesson test: The Second Law and the Carnot limit

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The Second Law and the Carnot limit

1.[2p]
Which statement is the Kelvin-Planck form of the Second Law?

No cycle can take heat from a single reservoir and produce an equal amount of work with no other effect

Correct

No cycle can transfer heat from a colder body to a hotter one with no other effect

The answer is: No cycle can take heat from a single reservoir and produce an equal amount of work with no other effect

Energy can be neither created nor destroyed

The answer is: No cycle can take heat from a single reservoir and produce an equal amount of work with no other effect

The entropy of an isolated system never decreases

The answer is: No cycle can take heat from a single reservoir and produce an equal amount of work with no other effect

2.[1p]
A refrigerator moving heat from a cold interior to a warm kitchen violates the Clausius statement.

True

The answer is: False

False

Correct

3.[3p]
In the proof that a Clausius violator implies a Kelvin-Planck violator, why can the cold reservoir be disconnected?

The engine rejects to it exactly the heat the violating device removes from it, so it nets zero

Correct

Its temperature is chosen to be absolute zero

The answer is: The engine rejects to it exactly the heat the violating device removes from it, so it nets zero

The violating device needs no work input

The answer is: The engine rejects to it exactly the heat the violating device removes from it, so it nets zero

The engine is reversible, so its heat exchange with the cold reservoir cancels itself

The answer is: The engine rejects to it exactly the heat the violating device removes from it, so it nets zero

4.[2p]
Carnot's theorem implies that a reversible engine's efficiency depends on

the two reservoir temperatures only

Correct

the working substance and the two temperatures

The answer is: the two reservoir temperatures only

the size of the engine and the heat supplied

The answer is: the two reservoir temperatures only

the pressure ratio of the cycle

The answer is: the two reservoir temperatures only

5.[2p]
Put the four stages of the Carnot cycle in order, starting from contact with the hot reservoir.

Isothermal compression at $T_{C}$
Adiabatic expansion falling to $T_{C}$
Isothermal expansion at $T_{H}$
Adiabatic compression back to $T_{H}$

Show the answer

a, b, c, d

6.[2p]
A reversible engine runs between reservoirs at $600$ degrees Celsius and $30$ degrees Celsius. What is its efficiency, as a percentage?

CorrectNot quite: 65.3

7.[2p]
A reversible heat pump keeps a house at $294.15$ K using outside air at $275.15$ K. What is its coefficient of performance?

CorrectNot quite: 15.5

8.[2p]
Which of these are sources of irreversibility?

Select all that apply

Friction between a piston and its cylinder

Correct

Expansion of a gas into an evacuated chamber

Correct

Heat flowing across a finite temperature difference

Correct

Compression of a gas along a quasi-static path with no friction

The answer is: Friction between a piston and its cylinder, Expansion of a gas into an evacuated chamber, Heat flowing across a finite temperature difference

9.[3p]
A real steam plant falls well short of the Carnot figure computed from its peak steam temperature. Which reason accounts for the largest part of the gap?

Heat is added from feedwater temperature upward, so the mean temperature of heat addition is far below the peak

Correct

The turbine blades are not perfectly smooth

The answer is: Heat is added from feedwater temperature upward, so the mean temperature of heat addition is far below the peak

The generator wastes power as heat in its windings

The answer is: Heat is added from feedwater temperature upward, so the mean temperature of heat addition is far below the peak

Some steam leaks from the seals

The answer is: Heat is added from feedwater temperature upward, so the mean temperature of heat addition is far below the peak

1.[2p] Which statement is the Kelvin-Planck form of the Second Law?

2.[1p] A refrigerator moving heat from a cold interior to a warm kitchen violates the Clausius statement.

3.[3p] In the proof that a Clausius violator implies a Kelvin-Planck violator, why can the cold reservoir be disconnected?

4.[2p] Carnot's theorem implies that a reversible engine's efficiency depends on

5.[2p] Put the four stages of the Carnot cycle in order, starting from contact with the hot reservoir.

6.[2p] A reversible engine runs between reservoirs at 600 degrees Celsius and 30 degrees Celsius. What is its efficiency, as a percentage?

7.[2p] A reversible heat pump keeps a house at 294.15 K using outside air at 275.15 K. What is its coefficient of performance?

8.[2p] Which of these are sources of irreversibility?

9.[3p] A real steam plant falls well short of the Carnot figure computed from its peak steam temperature. Which reason accounts for the largest part of the gap?

1.[2p]
Which statement is the Kelvin-Planck form of the Second Law?

2.[1p]
A refrigerator moving heat from a cold interior to a warm kitchen violates the Clausius statement.

3.[3p]
In the proof that a Clausius violator implies a Kelvin-Planck violator, why can the cold reservoir be disconnected?

4.[2p]
Carnot's theorem implies that a reversible engine's efficiency depends on

5.[2p]
Put the four stages of the Carnot cycle in order, starting from contact with the hot reservoir.

6.[2p]
A reversible engine runs between reservoirs at $600$ degrees Celsius and $30$ degrees Celsius. What is its efficiency, as a percentage?

7.[2p]
A reversible heat pump keeps a house at $294.15$ K using outside air at $275.15$ K. What is its coefficient of performance?

8.[2p]
Which of these are sources of irreversibility?

9.[3p]
A real steam plant falls well short of the Carnot figure computed from its peak steam temperature. Which reason accounts for the largest part of the gap?