On a p–V diagram, which physical quantity is plotted on the vertical axis and which on the horizontal axis?

Pressure is plotted on the vertical axis and volume on the horizontal axis.

What does a p–V diagram represent?

It represents thermodynamic processes by showing how pressure and volume of a system change.

Why do different thermodynamic processes appear as different shapes on a p–V diagram?

Because each process has a characteristic relationship between pressure and volume changes, producing distinct curves or lines that reflect how these quantities vary relative to each other.

What does the shape of a curve on a p–V diagram indicate about a thermodynamic process?

It indicates how pressure and volume change relative to each other during the process.

How is the work done by a gas during expansion or compression related to a p–V diagram?

The work done equals the area under the curve on the p–V diagram.

Explain why the area under a p–V curve represents work done.

Work done is the integral of pressure with respect to volume (W = ∫p dV), and this integral corresponds geometrically to the area between the curve and the volume axis.

AQA A-Level Physics 7408

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Engineering Physics

The p–V diagram

3 things to know
Paper 3, section B

Overview

Reading work from the area under a curve, cyclic processes, and the direction of the loop.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

What do the symbols in W = pΔV mean, and what does an anticlockwise loop indicate?

Process

What is a cyclic process, how is the work done in a single process found from a p–V diagram, and how is the net work per cycle found?

Process

If a cyclic process traces a clockwise loop on a p–V diagram, is net work done by the gas or on the gas?

Questions from this subtopic

Each one with the model answer underneath.

1
On a p–V diagram, which physical quantity is plotted on the vertical axis and which on the horizontal axis?
Model answer
Pressure is plotted on the vertical axis and volume on the horizontal axis.
2
What does a p–V diagram represent?
Model answer
It represents thermodynamic processes by showing how pressure and volume of a system change.
3
Why do different thermodynamic processes appear as different shapes on a p–V diagram?
Model answer
Because each process has a characteristic relationship between pressure and volume changes, producing distinct curves or lines that reflect how these quantities vary relative to each other.
4
What does the shape of a curve on a p–V diagram indicate about a thermodynamic process?
Model answer
It indicates how pressure and volume change relative to each other during the process.
5
How is the work done by a gas during expansion or compression related to a p–V diagram?
Model answer
The work done equals the area under the curve on the p–V diagram.
6
Explain why the area under a p–V curve represents work done.
Model answer
Work done is the integral of pressure with respect to volume (W = ∫p dV), and this integral corresponds geometrically to the area between the curve and the volume axis.

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