NCERT Book Class 11 Physics Chapter 11 Thermodynamics

CHAPTER ELEVEN

THERMODYNAMICS

11.1 INTRODUCTION
In previous chapter we have studied thermal properties of
matter. In this chapter we shall study laws that govern
thermal energy. We shall study the processes where work is
11.1 Introduction
converted into heat and vice versa. In winter, when we rub
11.2 Thermal equilibrium our palms together, we feel warmer; here work done in rubbing
11.3 Zeroth law of produces the ‘heat’. Conversely, in a steam engine, the ‘heat’
Thermodynamics of the steam is used to do useful work in moving the pistons,
11.4 Heat, internal energy and which in turn rotate the wheels of the train.
work In physics, we need to define the notions of heat,
11.5 First law of temperature, work, etc. more carefully. Historically, it took a
thermodynamics long time to arrive at the proper concept of ‘heat’. Before the
11.6 Specific heat capacity modern picture, heat was regarded as a fine invisible fluid
11.7 Thermodynamic state filling in the pores of a substance. On contact between a hot
variables and equation of body and a cold body, the fluid (called caloric) flowed from
state the colder to the hotter body ! This is similar to what happens
11.8 Thermodynamic processes when a horizontal pipe connects two tanks containing water
11.9 Second law of up to different heights. The flow continues until the levels of
thermodynamics water in the two tanks are the same. Likewise, in the ‘caloric’
11.10 Reversible and irreversible picture of heat, heat flows until the ‘caloric levels’ (i.e., the
processes temperatures) equalise.
11.11 Carnot engine In time, the picture of heat as a fluid was discarded in
favour of the modern concept of heat as a form of energy. An
Summary
important experiment in this connection was due to Benjamin
Points to ponder
Thomson (also known as Count Rumford) in 1798. He
Exercises
observed that boring of a brass cannon generated a lot of
heat, indeed enough to boil water. More significantly, the
amount of heat produced depended on the work done (by the
horses employed for turning the drill) but not on the
sharpness of the drill. In the caloric picture, a sharper drill
would scoop out more heat fluid from the pores; but this
was not observed. A most natural explanation of the
observations was that heat was a form of energy and the
experiment demonstrated conversion of energy from one form
to another–from work to heat.