Introduction

Orientation

Thermodynamics is the branch of physics that deals with the concepts of heat and temperature and the inter-conversion of heat and other forms of energy. In Std XI you studied the thermal properties of matter; here you study the laws that govern thermal energy itself, and in particular the processes in which work is converted into heat and heat into work.

The everyday observations behind it are familiar: a vehicle's engine warms up as it runs, and so do your muscles when you exercise. In both cases work is being done and heat is being produced, which suggests that heat should also be able to do work. That two-way conversion is the subject of the whole chapter.

Historically, the decisive evidence came in 1798, when Benjamin Thomson noticed that boring brass cannon produced enough heat to boil water, that the heat produced was related to the work done in turning the drill, and that it depended on how long the drill bored rather than on how sharp it was. The older theory, which treated heat as a fluid, predicted the opposite. Heat had to be a form of energy.

What This Chapter Covers

• Thermodynamic systems, their surroundings, and thermodynamic state variables.
• Thermodynamic processes and their $p$–$V$ diagrams.
• The zeroth, first and second laws of thermodynamics.
• The most useful applications: heat engines, refrigerators and heat pumps, and their efficiency.

This section carries no formula and is not set as a question in its own right; treat it as the frame for everything that follows.