PV Diagrams & Work Conceptual Cycles Quiz

9th Grade

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By Thames

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| Questions: 20 | Updated: Mar 6, 2026

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1. On a pressure–volume (PV) diagram, the work done by a gas is related to:

The slope of the curve only

The highest pressure only

The area under the curve

The colour of the curve

Concept: PV work equals area under the curve. Work is W = ∫PdV, which is the area under the curve. On a PV graph, a bigger area under the path means more work done by the gas.

Explanation

Concept: PV work equals area under the curve. Work is W = ∫PdV, which is the area under the curve. On a PV graph, a bigger area under the path means more work done by the gas.

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About This Quiz

Pv Diagrams & Work Conceptual Cycles Quiz - Quiz

This assessment focuses on PV diagrams and the work concept in thermodynamic cycles. It evaluates understanding of pressure-volume relationships, work done during processes, and the implications of these concepts in real-world applications. This knowledge is essential for students and professionals in physics and engineering, enhancing their ability to analyze energy... see moresystems effectively. see less

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2. If volume increases during a process (expansion), the work done by the gas is usually positive.

True

False

Concept: Expansion means the gas does work outward. Expansion means the gas pushes outward and does work on surroundings. With positive pressure and increasing volume, the PV work is typically positive.

Explanation

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3. If a gas is compressed (volume decreases), the work done by the gas is typically:

Positive

Negative

Zero

Always 1 J

Concept: Compression means work is done on the gas. Compression means work is done on the gas, so work by the gas is negative. The surroundings push the piston inward, transferring energy to the gas.

Explanation

Concept: Compression means work is done on the gas. Compression means work is done on the gas, so work by the gas is negative. The surroundings push the piston inward, transferring energy to the gas.

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4. A closed loop on a PV diagram represents a ______.

Concept: A loop returns to the start state. A loop means the system returns to the initial state. The path closes because both P and V return to their starting values.

Explanation

Concept: A loop returns to the start state. A loop means the system returns to the initial state. The path closes because both P and V return to their starting values.

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5. The net work done over a full PV cycle is represented by:

The tallest point of the loop

The width of the loop only

The area enclosed by the loop (with sign)

The average pressure only

Concept: Enclosed area = net work for a cycle. The enclosed area is net work; direction sets the sign. Clockwise vs counterclockwise determines whether the gas does net work or has work done on it.

Explanation

Concept: Enclosed area = net work for a cycle. The enclosed area is net work; direction sets the sign. Clockwise vs counterclockwise determines whether the gas does net work or has work done on it.

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6. A clockwise PV loop usually indicates positive net work done by the gas.

True

False

Concept: Clockwise loop = net expansion work. Clockwise direction corresponds to net expansion work. The gas tends to expand at higher pressure and compress at lower pressure, giving positive net area.

Explanation

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7. If a PV cycle is counterclockwise, the net work done by the gas is:

Positive

Negative

Zero

Cannot be determined

Concept: Counterclockwise loop = net work input. Counterclockwise typically indicates net work done on the gas. That’s common in refrigeration-type cycles where work must be supplied.

Explanation

Concept: Counterclockwise loop = net work input. Counterclockwise typically indicates net work done on the gas. That’s common in refrigeration-type cycles where work must be supplied.

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8. Which process has zero PV work?

Expansion at constant pressure

Compression at constant pressure

Change at constant volume

Change at constant pressure

Concept: No volume change means no PV work. If ΔV=0, then W=∫PdV=0. On a PV diagram, this corresponds to a vertical line.

Explanation

Concept: No volume change means no PV work. If ΔV=0, then W=∫PdV=0. On a PV diagram, this corresponds to a vertical line.

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9. A vertical line on a PV diagram (constant volume) corresponds to zero work.

True

False

Concept: Vertical line means ΔV=0. No change in volume means no PV work. Even if pressure changes, the area under the curve is zero because there is no horizontal width.

Explanation

Concept: Vertical line means ΔV=0. No change in volume means no PV work. Even if pressure changes, the area under the curve is zero because there is no horizontal width.

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10. A horizontal line on a PV diagram indicates:

Constant volume

Constant pressure

Constant temperature always

Zero heat transfer always

Concept: Horizontal line = constant pressure. Horizontal means pressure stays the same. Work can still be done because volume changes along the horizontal line.

Explanation

Concept: Horizontal line = constant pressure. Horizontal means pressure stays the same. Work can still be done because volume changes along the horizontal line.

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11. In a cycle, the net work done equals the net heat transfer because ΔU=___.

Concept: First law over a complete cycle. Over a cycle, ΔU=0, so net Q=net W. Any net heat added must appear as net work output (or vice versa).

Explanation

Concept: First law over a complete cycle. Over a cycle, ΔU=0, so net Q=net W. Any net heat added must appear as net work output (or vice versa).

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12. A gas completes a cycle and does net work of 200 J. The net heat added to the gas over the cycle is:

-200 J

0 J

+200 J

+400 J

Concept: Net Q equals net W for cycles. Over a cycle, net Q=net W. If the gas does +200 J of net work, it must have received +200 J of net heat overall.

Explanation

Concept: Net Q equals net W for cycles. Over a cycle, net Q=net W. If the gas does +200 J of net work, it must have received +200 J of net heat overall.

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13. The net heat transfer over a cycle must always be zero.

True

False

Concept: Cycles can have net heat input and net work output. Net heat can be positive if the system produces net work. The only quantity that must be zero over a cycle is ΔU.

Explanation

Concept: Cycles can have net heat input and net work output. Net heat can be positive if the system produces net work. The only quantity that must be zero over a cycle is ΔU.

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14. Which statement best matches a heat engine on a PV diagram?

It must have zero enclosed area

It typically forms a loop with positive net area (clockwise)

It must be a straight line

It must be a vertical line only

Concept: Heat engines produce net work. Engines produce net work, shown by positive loop area. This typically appears as a clockwise loop on the PV diagram.

Explanation

Concept: Heat engines produce net work. Engines produce net work, shown by positive loop area. This typically appears as a clockwise loop on the PV diagram.

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15. Which changes could reduce the area enclosed by a real PV cycle?

Friction and losses

Heat leaking out in unwanted ways

Making the cycle perfectly reversible

Pressure drops in valves/flow

Concept: Losses reduce useful PV work. Losses reduce effective pressure/volume work and shrink loop area. Making the cycle more reversible reduces losses, which would tend to increase, not reduce, the useful area.

Explanation

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16. If the loop area is smaller, the net work output is generally:

Larger

The same

Smaller

Negative always

Concept: Net work scales with enclosed area. Smaller area means less net work. A PV diagram is a direct visual way to compare work output between cycles.

Explanation

Concept: Net work scales with enclosed area. Smaller area means less net work. A PV diagram is a direct visual way to compare work output between cycles.

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17. You can have a cycle with net negative work (work done on the gas), such as a refrigeration cycle.

True

False

Concept: Refrigeration requires work input. Refrigerators require work input, so net work by gas can be negative. On a PV plot, this often appears as a counterclockwise loop.

Explanation

Concept: Refrigeration requires work input. Refrigerators require work input, so net work by gas can be negative. On a PV plot, this often appears as a counterclockwise loop.

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18. A refrigerator cycle is often represented on a PV diagram as:

A clockwise loop

A counterclockwise loop

A single point

A vertical line only

Concept: Counterclockwise loop = work input. Refrigeration requires net work input, typically counterclockwise. This indicates the surroundings do net work on the working substance.

Explanation

Concept: Counterclockwise loop = work input. Refrigeration requires net work input, typically counterclockwise. This indicates the surroundings do net work on the working substance.

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19. “Area under the curve” means area under the PVs ______ graph.

Concept: PV diagram axes. PV diagram is pressure vs volume. The “area” refers to the region under the curve on the P-V plot.

Explanation

Concept: PV diagram axes. PV diagram is pressure vs volume. The “area” refers to the region under the curve on the P-V plot.

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20. Best summary of PV diagrams for cycles:

PV graphs measure mass directly

Loops show cycles and enclosed area shows net work

Lines show only temperature

PV graphs ignore work completely

Concept: Two key PV ideas. The core ideas are loop = cycle and area = work. PV diagrams are useful because they visually connect process paths to mechanical work.

Explanation

Concept: Two key PV ideas. The core ideas are loop = cycle and area = work. PV diagrams are useful because they visually connect process paths to mechanical work.

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