PV-diagrams and expansion work | Thermodynamics | Physics | Khan Academy

TL;DR

Work done by a system can be calculated as the pressure times the change in volume, and the area under the curve in a PV-diagram represents the work done by or on the system.

Transcript

In the last video, we saw that a system could do work by expanding. And in the situation we drew, we had a situation where the ceiling was movable. We had this piston and we, like in our process video, we had a bunch of pebbles. We removed a pebble, so the pressure in our system, if we assume that it was just so small that the pressure was constant... Read More

Key Insights

• 💦 Work done by a system can be determined by multiplying the pressure by the change in volume.
• 💦 The area under the curve in a PV-diagram represents the work done by or on the system.
• 💦 The direction of the curve in a PV-diagram determines whether work is done by or on the system.
• 💦 The net work done in a closed loop in a PV-diagram represents the total work done by the system.
• 🤪 The internal energy of a system remains constant when going from one state to another, regardless of the path taken.
• 💦 The PV-diagram is a useful tool for understanding thermodynamic processes and calculating work.
• ❓ Calculus can be used to find the exact area under the curve in a PV-diagram.

Questions & Answers

Q: How is work calculated in thermodynamics?

Work in thermodynamics can be calculated by multiplying the pressure by the change in volume. This gives the amount of force applied by the system.

Q: What does the area under the curve in a PV-diagram represent?

The area under the curve in a PV-diagram represents the work done by the system. It can be calculated by finding the integral of pressure with respect to volume.

Q: Can the direction of the curve in a PV-diagram affect the work done?

Yes, the direction of the curve in a PV-diagram determines whether the work is done by or on the system. An increasing volume represents work done by the system, while a decreasing volume represents work done on the system.

Q: What is the significance of the net work done in a closed loop in a PV-diagram?

The net work done in a closed loop in a PV-diagram represents the total work done by the system. It is calculated by finding the area inside the loop and subtracting any work done on the system.

Summary & Key Takeaways

• Work done by a system can be determined by multiplying the pressure by the change in volume.

• The area under the curve in a PV-diagram represents the work done by the system.

• The work done on the system can be calculated by finding the area under the curve in the opposite direction.