Detailed Notes on Thermodynamics for the JEE Exam [Toppers’ Perspective]

1. Thermodynamic Processes

• Definition: A thermodynamic process is a sequence of changes in the state of a system, involving transfer of heat, work, or both, between the system and its surroundings.

Types of Processes:

• Isothermal: Temperature (T) remains constant during the process.
• Adiabatic: No heat transfer occurs between the system and its surroundings (Q = 0).
• Isobaric: Pressure (P) remains constant during the process.
• Isochoric: Volume (V) remains constant during the process.

2. Work Done in Isothermal Processes

• Formula: $$W = -PΔV$$, where W is the work done, P is the pressure, and ΔV is the change in volume.
• Interpretation: Work done in an isothermal expansion is negative, indicating work done by the system on the surroundings. Conversely, work done in an isothermal compression is positive, indicating work done on the system by the surroundings.
• Pressure-Volume Graph: In an isothermal process, the pressure-volume graph is a rectangular hyperbola.

3. Work Done in Adiabatic Processes

• Formula: $$W = -ΔU$$, where W is the work done and ΔU is the change in internal energy of the system.
• Interpretation: For an adiabatic expansion, ΔU is positive and work done is negative, implying work done by the system on the surroundings. For adiabatic compression, ΔU is negative and work done is positive, signifying work done on the system by the surroundings.
• Adiabatic Heating and Cooling: During adiabatic compression, internal energy increases, leading to an increase in temperature (adiabatic heating). Conversely, during adiabatic expansion, internal energy decreases, resulting in a drop in temperature (adiabatic cooling).

4. Work Done in Isobaric Processes

• Formula: $$W = PΔV$$, where W is the work done, P is the constant pressure, and ΔV is the change in volume.
• Interpretation: Work done in an isobaric expansion is positive, indicating work done by the system on the surroundings. Similarly, work done in an isobaric compression is negative, representing work done on the system by the surroundings.
• Significance: Pressure-volume work plays a crucial role in isobaric processes, as the work done is directly proportional to the change in volume.

5. Work Done in Isochoric Processes

• Formula: $$W = 0$$ since there is no change in volume (ΔV = 0) at constant volume.
• Interpretation: No macroscopic work is done during an isochoric process.
• Examples: Isochoric heating (increasing internal energy) and isochoric cooling (decreasing internal energy) without volume changes.

6. Heat and Internal Energy

• Relationship: Heat added to a system (Q) is equal to the change in its internal energy (ΔU) for various processes, expressed as Q = ΔU.
• Specific Heat Capacity: The amount of heat required to raise the temperature of a unit mass of a substance by 1°C is known as its specific heat capacity.

7. Applications and Problem-Solving

• Analyze thermodynamic systems, predict their behavior, and solve complex numerical problems involving work done, heat transfer, and internal energy changes in different thermodynamic processes.
• Practice a wide range of numerical problems to reinforce understanding and enhance problem-solving skills.

Recommended NCERT Textbooks:

• NCERT Physics Part 1 (Class 11) - Chapter 12: Thermodynamics
• NCERT Physics Part 2 (Class 12) - Chapter 5: Thermodynamics

By comprehensively mastering these concepts, you’ll be well-equipped to tackle the thermodynamics section of the JEE exam and improve your chances of securing a high score.