Maharashtra Board Class 12 Physics Chapter 4 Thermodynamics PDF Download

Thermodynamics

Can You Recall?

1. When a piece of ice is placed in water at room temperature, the ice melts and water cools down. Why does their temperature change?

2. When water boils, why does its temperature remains constant?

3. When an inflated balloon is suddenly burst, why is the emerging air slightly cooled?

Introduction

In XIth Standard, we have studied thermal properties of matter. In this chapter, we shall study the laws that govern the behavior of thermal energy. We shall study the processes where work is converted into heat and vice versa.

When we drive a vehicle, its engine gets warmer after some time. Similarly, when we exercise, we also feel warmth in our body. Similar physics is involved in both the cases. The engine of a vehicle as well as our muscles do some work and both produce some heat. It is, therefore, natural to think that if the work done by an engine or our muscles produces some heat then heat should also be able to do some work. Thermodynamics is mostly the study of conversion of work (or any form of energy) into heat and the other way round.

When a hot object is in contact with a cold object, we notice that both objects reach the same temperature after some time. The hot object gets cooler and the cold object becomes warmer. That means something is exchanged between the two objects. This something is heat. According to modern theory, heat is a form of energy.

In the year 1798 it was observed by Benjamin Thomson, a British scientist, that tremendous heat is produced when brass canons were bored. The heat thus produced was large enough to boil water. A very important observation was that the amount of heat produced was related to the work done in turning the drill that was used to bore the canon. It was also noticed that more heat was produced when the drill bored for a longer time. It did not depend on the sharpness of the drills used. A sharper drill would have removed more heat according to the older theory of heat, which assumed heat to be some form of a fluid. This observation could be explained only if heat was a form of energy and not any fluid. It is natural to conclude from these observations that energy can be converted from one form to another form. In this particular case, a very important law of physics can be proposed that, the work done by a system is converted into heat. The drills used to bore the canons do the work and the canons get heated up.

This was, probably, one of the pioneer experiments in thermodynamics. 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.

It is the field of study that allows us to understand nature of many of the fundamental interactions in the universe. It can explain phenomena as simple as water boiling in a vessel, and also something as complex as the creation of a new star. Thermodynamics is an important branch of physics having many practical applications.

In this chapter we will try to understand a thermodynamic system, thermodynamic variables, thermodynamic processes and the laws that govern these processes. We will also study the most important and useful applications of thermodynamics, the heat engines and their efficiency.

Teacher's Note

Thermodynamics is everywhere in your life. When you cook food in a pressure cooker at home, you are using thermodynamics. The heat and pressure work together to cook the food faster.

Exam Trick

Remember: Heat and work are both forms of energy transfer. If a system gets hotter, either heat went in or work was done on it (like rubbing your hands together makes them hot).

Points to Remember

Heat is energy that transfers between objects at different temperatures.
Work is done when a force moves an object.
Energy can change from one form to another.
The drills boring cannons showed heat comes from work, not from a fluid.
Thermodynamics explains simple things like boiling water and complex things like stars.

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