NEET Physics: Waves – NCERT Masterclass & 100 MCQ Quiz

THERMODYNAMICS: COMPLETE NCERT MODULE

1. Introduction to 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 a macroscopic science, meaning it deals with bulk systems and does not go into the molecular constitution of matter.

Real-Life Example: In winter, when we rub our palms together, we feel warmer; here mechanical work produces 'heat'. Conversely, in a steam engine, the 'heat' of the steam is used to do useful work in moving the pistons.

2. Thermal Equilibrium & Zeroth Law

The state of a system is an equilibrium state if the macroscopic variables that characterise the system (like pressure, volume, temperature) do not change in time. The Zeroth Law states: "Two systems in thermal equilibrium with a third system separately are in thermal equilibrium with each other."

Significance: The Zeroth Law formally provides the definition of Temperature (T). It is the thermodynamic variable whose value is equal for systems in thermal equilibrium.

3. Internal Energy, Heat, and Work

• Internal Energy (U): The sum of random molecular kinetic and potential energies in the rest frame of the system. It is a state variable, depending only on the state, not on the path taken to arrive at that state.
• Heat (Q): Energy transfer caused by a temperature difference between the system and its surroundings.
• Work (W): Energy transfer brought about by mechanical means, such as moving a piston.

4. The First Law of Thermodynamics

This law is the general law of conservation of energy applied to any thermal system.

$$\Delta Q = \Delta U + \Delta W$$

Where heat supplied to the system ($\Delta Q$) goes partly into increasing internal energy ($\Delta U$) and the rest into work on the environment ($\Delta W$).

📌 NEET Essentials: Sign Conventions

• Heat supplied to the system: $+\Delta Q$
• Heat removed from the system: $-\Delta Q$
• Work done BY the system (Expansion): $+\Delta W$
• Work done ON the system (Compression): $-\Delta W$

5. Thermodynamic Processes

• Isothermal: Occurs at a constant temperature. For an ideal gas, internal energy depends only on temperature, so $\Delta U = 0$.
• Adiabatic: No heat flow between the system and surroundings ($\Delta Q = 0$).
• Isochoric: Volume is constant. Since $\Delta V = 0$, work done ($P\Delta V$) is zero. All heat goes to internal energy.
• Isobaric: Pressure remains constant while volume and temperature change.

6. Carnot Engine & Efficiency

A reversible heat engine operating between two temperatures $T_1$ (source) and $T_2$ (sink) is called a Carnot engine. It has the maximum possible efficiency.

$$\eta = 1 - \frac{T_2}{T_1}$$

← Back to NEET Resource Hub

🚀 NEET THERMODYNAMICS MEGA QUIZ (100 MCQ)

Solve the 5 parts below to master Laws, Processes, and Engines.

← Back to NEET Resource Hub