Class 11 Physics Ch 12

 Thermodynamics Class 11 Physics Chapter 12 notes 

Thermodynamics Engine

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Class 11 physics Chapter 12 Thermodynamics is an important study material for the Students who are presently studying in CBSE 11th standard.  This Chapter notes includes Introduction The conservation of energy and the fact that heat flows spontaneously from hot to cold bodies rather than the other way around are the foundations of thermodynamics. The study of heat and its conversion to mechanical energy is referred to as thermodynamics. It is derived from a Greek word that means "Heat Movement." In this chapter, we will look at thermodynamic laws, different thermodynamic processes, and the basic theory of a heat engine, refrigerator, and Carnot engine.

Key Notes for CBSE NCERT based Class 11th Physics

 Class 11 Physics Solutions are matter experts according to the latest CBSE Syllabus 2023-24 and its marking schemes. Thermodynamics  Physics Class twelve NCERT PDF can come easy to understand  while preparing notes and during  different Exams. Download Class 11 Physics Chapter Thermodynamics Notes
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CBSE Class 11 Physics Chapter 12 Thermodynamics Notes   


It is that branch of physics which deals with concepts of heat and temperature and their relation to energy and work

Thermal Equilibrium: 

Two systems are said to be in thermal equilibrium if the temperatures of the two systems are equal. In mechanics if the net force on a system is zero, the system is in equilibrium.

⚫ In Thermodynamics equilibrium means all the macroscopic variables (pressure

temperature and volume) don't change with time. They are constant throughout System and Surroundings

System: System is defined as any part of universe enclosed by some exchange of heat or energy takes place,

Surroundings: Any part of the universe which is not a system.

For example: - If we consider a hot coffee in a cup then the cup is the system and boundary through which


everything else is the surroundings. System and surroundings constitute Universe

Types of Systems

1. Open System: In this system there is exchange of energy and matter. For Example:- Water boils in a pan without lid, a cup of coffee

2. Closed System: In this system exchange of matter does not take place but exchange of energy takes place. For Exemple: A balloon filled with gas. 3. Isolated System: Infic system there is neither change in matter nor change in energy. For

1. Adiabatic wall-It is an insulating wall which doesn't allow heat to flow from one system to another. This means temperature of both the systems won't change with 

For example:- Thermos Flask.

2. Diathermic Wall: It is a conducting wall which allows the flow of heat between any 2 systems.

For example:-Hot tea in a cup.

Zeroth Law of Thermodynamics: Zeroth law of thermodynamics states that when two systems are in thermal equilibrium through a third system separately then they are in thermal equilibrium with each other. Systems A and B are in thermal equilibrium with C. Then they will be in equilibrium with each other.

Thermodynamic state variables: Thermodynamic state variables are the macroscopic quantities which determine the thermodynamic equilibrium state of a system.

Types of thermodynamic state variables: -

1. Extensive variables: Extensive variables are those that depend on the mass of the system or the number of particles in the system. Example: volume, mass internal energy

2. Intensive variables: They don't depend on size of the system

Example: Pressure and Temperature are known as Intensive Variables 

Equation of State: Equation of State depicts the relationship between the state variables

96.0 v4 83

Example: Pressure and Temperature are known as intensive variables. (pressure, mass, volume, density).

• Consider an ideal gas the equation of

PV=NRT where

⚫ P. V and Tare state variables and number of moles

Internal Energy (U): is defined as the sum of kinetic energies and potential energies of the molecules constiting energy.

⚫ It is an extensive variable as it depends on the size of the system.

• It can be specified by values of pressure, volume and temperature at that particular time. 

Two different modes to change Internal energy are:- 

Heat and Work

1. Heat: 

Due to transfer of heat kinetic energy and potential energy changes from bottle to the balloon. This results in the change of internal energy.

2. Work:- 

We can do some work on the system as a result the internal energy of the system changes.

Internal energy increases when the system absorbs heat and some work is done on the system similarly internal energy decreases if we change the conditions.

How Internal energy is different from Work and Heat

Heat and work are not state variables unlike internal energy.

⚫They are modes of energy transfer to system resulting in change in internal energy.

First Law of Thermodynamics: The change in the internal energy of a closed system is equal to the amount of heat supplied to the system, minus the amount of work done by the system on its surroundings.

Mathematically: AQ=AU+AW

Where: AQ is the heat supplied to the system by the surroundings

• AW is the work done by the system by the surroundings 

⚫ AU is the change in internal energy of the system

AQ-AW AU where (AQ and AW are path dependent quantities whereas AU is path independent quantity) 


Case 1:- System undergoes a process such that which means internal energy is constant.

⚫ this means heat supplied by the surroundings is equal to the work done by the system on the surroundings. Case 2: System is a gas in a  linder with movable piston, by moving the piston we can change the volume of the gas, downwards some work is done and it can be given as:-

=Px Area x displacement

AW PAV (AV= Area x displacement)

⚫ Therefore by first law of thermodynamicsbAQ = AU PAV where AV= change in volume Specific heat capacity (s): Specific heat is defined as the amount of heat required to raise the temperature of a body per unit mass: 

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