DC Pandey Laws of Thermodynamics Solutions

DC Pandey Waves and Thermodynamics Solutions Chapter 18 ‘Laws of Thermodynamics’ have been prepared to guide you to solve the thermodynamic numerical questions easily. You will get to develop a foundational base in physical sciences for Class 11 and Class 12 by studying important terms discussed in this chapter. This Chapter of DC Pandey Physics Book Solutions includes the laws of thermodynamics and thermodynamic processes. By learning how to evaluate the efficiency of a cycle, you will be able to understand the application of these concepts on Heat Engines and Refrigerators. You will also learn the zeroeth law of thermodynamics, second law of thermodynamics, reversible and irreversible processes.

DC Pandey Laws of Thermodynamics for Class 11 and Class 12 include 124 questions arranged systematically in 3 introductory exercises and 2 exercises for JEE Main, and JEE Advanced. Our solutions for DC Pandey Laws of Thermodynamics will help you learn to manage your time efficiently in the exam hall by practising the most frequently occurring pattern of questions in the competitive exams such as NEET and JEE. There will be a significant boost in your competency by practising these questions thoroughly.

The solutions for DC Pandey Laws and Thermodynamics are provided in an interactive and inclusive manner. Our subject matter experts research extensively to address the most frequently occurring doubts in this chapter. Therefore, anytime you stumble upon a confusing topic, Instasolv can be your go-to platform where we will satisfy you with complete conceptual clarity. All the questions of the DC Pandey Waves and Thermodynamics book are covered in a step by step format with in-depth reasoning. 

Important Topics for DC Pandey Waves and Thermodynamics Solutions Chapter 18: Laws of Thermodynamics

Important Terms

  • Heat Transfer (Q):

Q=nCT such that T is the difference between final temperature Tf and initial temperature Ti of gas and C is the molar heat capacity.

When process PVx=constant then 

  • Internal Energy (U):

Where ΔU is the internal energy.

  • Work:

To find the work done by a system, we may find the area covered in the P-V graph where P is a function of V. It is given as

When volume is constant, work= 0

When volume is increasing, work done is positive

When volume is decreasing, work done is negative

First Law of Thermodynamics

This law states that ΔU=Q-W

When the work done is positive, work is done by the system on its surroundings

When the work done is negative, work is done on the system by the surroundings.

Thermodynamic Processes

  • Isothermal Process:

In an isothermal process, the temperature of the system remains constant.

Internal energy, ΔU=0

And work done is equal to heat transfer, 

  • Adiabatic Process:

When heat transfer from or into the system is zero, then the process is termed as an adiabatic process, i.e. Q=0.

  • Isobaric Process:

When the pressure remains constant in a process, it is termed as an isobaric process.

  • Isochoric Process:

When the volume remains constant in a process, it is termed as an isochoric process.

Work Done, W=0 and Heat Transfer is equal to the Internal energy,

Efficiency of a Cycle

In a cyclic process, internal energy remains zero while net work done is equal to the net heat transfer. Efficiency is the product of 100 and the ratio of work done with the heat supplied.

Heat Engines

Using a heat engine, we can convert heat energy into mechanical energy. Based on the type of cycles, heat engines are of 3 types which are Carnot engine, Diesel Engine, and Petrol Engine.


In a refrigerator, the work is done on a cold body to absorb its heat and return it to the source.

Zeroeth Law of Thermodynamics

According to the zeroeth law, if there are two bodies A and B which are in equilibrium with a system C, then the two bodies A and B will be in equilibrium with one another.

Second Law of Thermodynamics

  • Clausius Statement: It is impossible for heat transfer to take place from a cold body to a hot body.
  • Kelvin-Planck Statement: No heat engine can ever have 100% efficiency.
  • Entropy Statement: For any process, ΔS≥0

Reversible and Irreversible Processes

An irreversible process flows in one direction only, i.e., the initial conditions cannot be achieved. These processes remain out of equilibrium throughout their commencement.

A reversible process is also known as an equilibrium process because there is a state of equilibrium throughout the process.

Exercise Discussion for DC Pandey Waves and Thermodynamics Solutions Chapter 18: Laws of Thermodynamics

Introductory Exercises:

  • In exercise 18.1, questions about heat transfer, work, and internal energy are asked using the first law of thermodynamics.
  • Exercise 18.2 covers questions about different thermodynamic processes.
  • The efficiency of a cycle, heat engine, refrigerator, the zeroeth and second law of thermodynamics are covered in detail in Exercise 18.3.

Exercise for JEE Main:

  • In the subjective questions, you will be required to find the work done, heat transfer, and changes in internal energy. 
  • Also, you will get to study the graphs There are 53 objective multiple-choice questions in this exercise including problems based on graphs.
  • There are assertion-reasoning and match the column questions in these exercises besides the complex numerical problems covering the laws of thermodynamics thoroughly.

Why Use DC Pandey Waves and Thermodynamics Solutions Chapter 18: Laws of Thermodynamics by Instasolv?

  • You can rely on the accuracy of DC Pandey Waves and Thermodynamics Solutions for JEE by the Instasolv experts because we get these answers cross-checked at two stages.
  • We have covered all the important topics in a question-answer format with an in-depth explanation of each concept that is employed in these solutions.
  • You can refer to our DC Pandey Laws of Thermodynamics Solutions for Class 11 and Class 12 exams also.