Thermodynamics – Complete Notes for B.Sc. 1st Year Physics Students | BSC Physics Notes

Thermodynamics – Complete Notes for B.Sc. 1st Year Physics Students

🔹 Introduction

Thermodynamics is a fundamental branch of physics that deals with the study of heat, temperature, energy, and the work done by or on a system. It lays the foundation for understanding physical processes in everything from steam engines to black holes. For B.Sc. 1st Year Physics students, thermodynamics is a core topic that requires clarity of concepts, logical thinking, and application skills.

In this detailed note, you’ll find all the key principles, laws, derivations, examples, and applications of thermodynamics — making it a valuable resource for your exam preparation and deeper understanding.

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🔹 Basic Concepts and Definitions

1. System: A part of the universe selected for analysis. It can be:

   • Open system: Can exchange both energy and matter (e.g., human body)

   • Closed system: Can exchange energy but not matter (e.g., boiling water in a closed pot)

   • Isolated system: No exchange of matter or energy (e.g., insulated thermos)

2. Surroundings: Everything external to the system.

3. Boundary: The surface that separates the system from its surroundings.

4. State of a System: Defined by properties like pressure, temperature, volume, and internal energy.

5. Process: Change in the state of a system. Types include isothermal, adiabatic, isobaric, and isochoric.

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🔹 Zeroth Law of Thermodynamics

If system A is in thermal equilibrium with system B, and system B is in thermal equilibrium with system C, then system A is in thermal equilibrium with system C.

Importance: This law helps define the concept of temperature.

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🔹 First Law of Thermodynamics

Also known as the Law of Conservation of Energy.

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

Where:

• $\Delta Q$: Heat added to the system

• $\Delta U$: Change in internal energy

• $\Delta W$: Work done by the system

Special cases:

• Isothermal ($\Delta U = 0$) → $Q = W$

• Adiabatic ($Q = 0$) → $\Delta U = -W$

• Isochoric ($\Delta V = 0$) → $W = 0$

• Isobaric (constant pressure) → Work $W = P\Delta V$

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🔹 Second Law of Thermodynamics

The second law introduces the concept of entropy and defines the direction of thermodynamic processes.

Kelvin-Planck Statement: It is impossible to convert all heat into work in a cyclic process.

Clausius Statement: Heat cannot spontaneously flow from a colder body to a hotter one.

Entropy (S):

• A measure of disorder.

• For any irreversible process: $\Delta S > 0$

• For a reversible process: $\Delta S = 0$

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🔹 Third Law of Thermodynamics

As the temperature of a system approaches absolute zero, the entropy of a perfect crystal approaches zero:

$\lim_{T \to 0} S = 0$

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🔹 Thermodynamic Processes

1. Isothermal Process:

   • Temperature remains constant.

   • $\Delta U = 0$, $Q = W$

   • Example: Melting of ice at 0°C

2. Adiabatic Process:

   • No heat exchange (Q = 0)

   • $\Delta U = -W$

   • Example: Rapid compression/expansion in engines

3. Isochoric Process:

   • Volume remains constant

   • $W = 0$, $\Delta Q = \Delta U$

4. Isobaric Process:

   • Pressure remains constant

   • $W = P \Delta V$, $Q = \Delta U + P \Delta V$

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🔹 Specific Heat Capacity

Specific heat (C) is the amount of heat required to raise the temperature of 1 kg of substance by 1°C.

• At constant volume: $C_v$

• At constant pressure: $C_p$

Relation: $C_p - C_v = R$ (for ideal gases)

Molar specific heat:
$Q = n C \Delta T$

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🔹 Work Done in Thermodynamic Processes

1. Isothermal: $W = nRT \ln \frac{V_2}{V_1}$

2. Adiabatic: $W = \frac{P_2 V_2 - P_1 V_1}{\gamma - 1}$

3. Isochoric: $W = 0$

4. Isobaric: $W = P(V_2 - V_1)$

Where $\gamma = C_p / C_v$ is the adiabatic index.

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🔹 Heat Engines and Refrigerators

1. Heat Engine:

   • Converts heat into work

   • Efficiency: $\eta = \frac{W}{Q_1} = 1 - \frac{Q_2}{Q_1}$

2. Refrigerator:

   • Transfers heat from cold to hot reservoir

   • Coefficient of Performance: $\text{COP} = \frac{Q_2}{W}$

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🔹 Carnot Cycle

An idealized cycle with maximum possible efficiency.

• Two isothermal processes

• Two adiabatic processes

Efficiency of Carnot Engine:
$\eta = 1 - \frac{T_2}{T_1}$

Where $T_1$ and $T_2$ are absolute temperatures of source and sink.

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🔹 Real-Life Applications of Thermodynamics

• Engines (cars, trains, airplanes)

• Refrigerators and Air Conditioners

• Power Plants

• Meteorology (weather prediction)

• Chemical Reactions (enthalpy and entropy changes)

• Biological Systems (body temperature regulation)

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🔹 Important Numerical Problems

Q1: A gas does 300 J of work in an adiabatic expansion and its internal energy decreases by 200 J. Find the heat absorbed.

Solution: Q = ΔU + W = -200 + 300 = 100 J

Q2: Find the efficiency of a Carnot engine operating between 500 K and 300 K.

$\eta = 1 - \frac{T_2}{T_1} = 1 - \frac{300}{500} = 0.4 = 40$

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🔹 Tips for Exam Preparation

• Always remember which quantities are conserved (energy, entropy, etc.)

• Practice derivations step-by-step: First law, Carnot cycle, etc.

• Understand the physical meaning behind equations

• Solve previous year numerical problems

• Use concept maps for thermodynamic processes

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🔹 Summary

Thermodynamics connects theoretical physics to practical applications in daily life and industry. For B.Sc. 1st Year students, understanding these principles ensures a strong foundation in physical sciences.

Key points to remember:

• First law = Energy conservation

• Second law = Direction of processes, entropy

• Thermodynamic processes have unique equations

• Carnot cycle shows ideal efficiency

• Applications are widespread in science and engineering

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🔹 Final Words

Thermodynamics is more than just equations — it's about understanding how energy flows and governs the universe. By mastering these principles, you gain insight into systems ranging from engines to ecosystems.

If you found this helpful, share it with your friends and revisit before exams. Stay consistent, keep revising, and embrace the beauty of physics! 

BSC Physics Notes TU 1st year

Thermodynamics 

In this page you can find BSC Physics Handwritten notes for TU 1st year students.You can download pdf file below.

Also read Collision notes pdf

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