NCERT Class 11 Physics Physics Part-II: Chapter 4 — Thermodynamics
This chapter introduces Thermodynamics, the branch of physics dealing with heat, temperature, and the inter-conversion of energy. It contrasts the historical 'caloric' fluid theory with the modern understanding of heat as energy, citing Count Rumford's cannon-boring experiment as evidence for work-heat conversion. Thermodynamics is presented as a macroscopic science, describing systems using variables like pressure, volume, and temperature, rather than individual molecular behavior. The chapter distinguishes thermodynamic equilibrium from mechanical equilibrium, explaining that thermodynamic equilibrium involves time-invariant macroscopic variables. It also introduces the concepts of adiabatic and diathermic walls, which determine heat flow between systems and influence whether thermal equilibrium is reached.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 11 |
| Subject | Physics |
| Book | Physics Part-II |
| Chapter | Chapter 4 — Thermodynamics |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 6 minutes |
| Word count | 1022 |
Learning outcomes
- Understand the fundamental concepts of thermodynamics, including heat, temperature, and energy.
- Differentiate between the historical caloric theory and the modern concept of heat as energy.
- Recognize thermodynamics as a macroscopic science.
- Define and identify thermodynamic equilibrium.
- Understand the role of adiabatic and diathermic walls in heat transfer.
Vocabulary
| Word | Meaning |
|---|---|
| Thermodynamics | The branch of physics that deals with heat and temperature and the inter-conversion of heat and other forms of energy. |
| Caloric | An obsolete scientific theory that heat was a fluid substance. |
| Macroscopic | Visible or measurable by ordinary means; not microscopic. |
| Equilibrium | A state in which opposing forces or influences are balanced. |
| Adiabatic wall | An insulating wall that does not allow flow of heat. |
| Diathermic wall | A conducting wall that allows heat to flow from one system to another. |
| State variables | Macroscopic variables that characterise the state of a system, such as pressure, volume, and temperature. |
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Practice questions
- What is the main difference between the historical caloric theory and the modern concept of heat? Answer: The caloric theory viewed heat as a fluid, while the modern concept treats heat as a form of energy.
- Give an example of work being converted into heat. Answer: Rubbing palms together in winter generates heat due to the work done.
- What does it mean for a system to be in thermodynamic equilibrium? Answer: A system is in thermodynamic equilibrium when its macroscopic variables (like pressure, volume, temperature) do not change with time.
- What is the function of an adiabatic wall? Answer: An adiabatic wall prevents the flow of heat between systems.
Practice MCQs
Q1. Thermodynamics is a science that deals with:
Explanation: Thermodynamics specifically studies the concepts of heat, temperature, and the inter-conversion of heat with other forms of energy.
Q2. Benjamin Thomson's experiment with boring cannons demonstrated:
Explanation: Rumford's observations showed that the amount of heat produced was related to the work done, supporting the idea that heat is a form of energy.
Q3. Which of the following is NOT a macroscopic variable used to describe the state of a gas in thermodynamics?
Explanation: Thermodynamics uses macroscopic variables like pressure, volume, and temperature, avoiding detailed molecular descriptions.
Q4. A wall that allows heat to flow between two systems is called:
Explanation: A diathermic wall is a conducting wall that permits heat transfer between systems.
Q5. In mechanics, equilibrium means:
Explanation: Mechanical equilibrium is defined by the absence of net external forces and torques acting on the system.
Frequently asked questions
What is thermodynamics?
Thermodynamics is the branch of physics that deals with heat, temperature, and the inter-conversion of heat and other forms of energy.
What is the difference between mechanics and thermodynamics?
Mechanics deals with the motion of bodies under forces, while thermodynamics focuses on the internal macroscopic state of a body and energy transformations.
What does it mean for a system to be in thermodynamic equilibrium?
A system is in thermodynamic equilibrium when its macroscopic variables, such as pressure, volume, and temperature, remain constant over time.
What is the significance of Count Rumford's experiment?
Count Rumford's experiment demonstrated that heat is a form of energy and can be generated by doing work, challenging the caloric theory.
What is a diathermic wall?
A diathermic wall is a boundary between two systems that allows heat to pass through it.
What is an adiabatic wall?
An adiabatic wall is an insulating boundary that prevents the transfer of heat between systems.
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NCERT Class 11 Physics — Physics Part-II — Chapter 4 — Thermodynamics. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.