• Introduction to Thermodynamics
  • Introduction to Science and the Realm of Physics, Physical Quantities, and Units
  • 1.1 Physics: An Introduction
  • 1.2 Physical Quantities and Units
  • 1.3 Accuracy, Precision, and Significant Figures
  • 1.4 Approximation
  • Section Summary
  • Conceptual Questions
  • Problems & Exercises
  • Introduction to One-Dimensional Kinematics
  • 2.1 Displacement
  • 2.2 Vectors, Scalars, and Coordinate Systems
  • 2.3 Time, Velocity, and Speed
  • 2.4 Acceleration
  • 2.5 Motion Equations for Constant Acceleration in One Dimension
  • 2.6 Problem-Solving Basics for One-Dimensional Kinematics
  • 2.7 Falling Objects
  • 2.8 Graphical Analysis of One-Dimensional Motion
  • Introduction to Two-Dimensional Kinematics
  • 3.1 Kinematics in Two Dimensions: An Introduction
  • 3.2 Vector Addition and Subtraction: Graphical Methods
  • 3.3 Vector Addition and Subtraction: Analytical Methods
  • 3.4 Projectile Motion
  • 3.5 Addition of Velocities
  • Introduction to Dynamics: Newton’s Laws of Motion
  • 4.1 Development of Force Concept
  • 4.2 Newton’s First Law of Motion: Inertia
  • 4.3 Newton’s Second Law of Motion: Concept of a System
  • 4.4 Newton’s Third Law of Motion: Symmetry in Forces
  • 4.5 Normal, Tension, and Other Examples of Forces
  • 4.6 Problem-Solving Strategies
  • 4.7 Further Applications of Newton’s Laws of Motion
  • 4.8 Extended Topic: The Four Basic Forces—An Introduction
  • Introduction: Further Applications of Newton’s Laws
  • 5.1 Friction
  • 5.2 Drag Forces
  • 5.3 Elasticity: Stress and Strain
  • Introduction to Uniform Circular Motion and Gravitation
  • 6.1 Rotation Angle and Angular Velocity
  • 6.2 Centripetal Acceleration
  • 6.3 Centripetal Force
  • 6.4 Fictitious Forces and Non-inertial Frames: The Coriolis Force
  • 6.5 Newton’s Universal Law of Gravitation
  • 6.6 Satellites and Kepler’s Laws: An Argument for Simplicity
  • Introduction to Work, Energy, and Energy Resources
  • 7.1 Work: The Scientific Definition
  • 7.2 Kinetic Energy and the Work-Energy Theorem
  • 7.3 Gravitational Potential Energy
  • 7.4 Conservative Forces and Potential Energy
  • 7.5 Nonconservative Forces
  • 7.6 Conservation of Energy
  • 7.8 Work, Energy, and Power in Humans
  • 7.9 World Energy Use
  • Introduction to Linear Momentum and Collisions
  • 8.1 Linear Momentum and Force
  • 8.2 Impulse
  • 8.3 Conservation of Momentum
  • 8.4 Elastic Collisions in One Dimension
  • 8.5 Inelastic Collisions in One Dimension
  • 8.6 Collisions of Point Masses in Two Dimensions
  • 8.7 Introduction to Rocket Propulsion
  • Introduction to Statics and Torque
  • 9.1 The First Condition for Equilibrium
  • 9.2 The Second Condition for Equilibrium
  • 9.3 Stability
  • 9.4 Applications of Statics, Including Problem-Solving Strategies
  • 9.5 Simple Machines
  • 9.6 Forces and Torques in Muscles and Joints
  • Introduction to Rotational Motion and Angular Momentum
  • 10.1 Angular Acceleration
  • 10.2 Kinematics of Rotational Motion
  • 10.3 Dynamics of Rotational Motion: Rotational Inertia
  • 10.4 Rotational Kinetic Energy: Work and Energy Revisited
  • 10.5 Angular Momentum and Its Conservation
  • 10.6 Collisions of Extended Bodies in Two Dimensions
  • 10.7 Gyroscopic Effects: Vector Aspects of Angular Momentum
  • Introduction to Fluid Statics
  • 11.1 What Is a Fluid?
  • 11.2 Density
  • 11.3 Pressure
  • 11.4 Variation of Pressure with Depth in a Fluid
  • 11.5 Pascal’s Principle
  • 11.6 Gauge Pressure, Absolute Pressure, and Pressure Measurement
  • 11.7 Archimedes’ Principle
  • 11.8 Cohesion and Adhesion in Liquids: Surface Tension and Capillary Action
  • 11.9 Pressures in the Body
  • Introduction to Fluid Dynamics and Its Biological and Medical Applications
  • 12.1 Flow Rate and Its Relation to Velocity
  • 12.2 Bernoulli’s Equation
  • 12.3 The Most General Applications of Bernoulli’s Equation
  • 12.4 Viscosity and Laminar Flow; Poiseuille’s Law
  • 12.5 The Onset of Turbulence
  • 12.6 Motion of an Object in a Viscous Fluid
  • 12.7 Molecular Transport Phenomena: Diffusion, Osmosis, and Related Processes
  • Introduction to Temperature, Kinetic Theory, and the Gas Laws
  • 13.1 Temperature
  • 13.2 Thermal Expansion of Solids and Liquids
  • 13.3 The Ideal Gas Law
  • 13.4 Kinetic Theory: Atomic and Molecular Explanation of Pressure and Temperature
  • 13.5 Phase Changes
  • 13.6 Humidity, Evaporation, and Boiling
  • Introduction to Heat and Heat Transfer Methods
  • 14.2 Temperature Change and Heat Capacity
  • 14.3 Phase Change and Latent Heat
  • 14.4 Heat Transfer Methods
  • 14.5 Conduction
  • 14.6 Convection
  • 14.7 Radiation
  • 15.1 The First Law of Thermodynamics
  • 15.2 The First Law of Thermodynamics and Some Simple Processes
  • 15.3 Introduction to the Second Law of Thermodynamics: Heat Engines and Their Efficiency
  • 15.4 Carnot’s Perfect Heat Engine: The Second Law of Thermodynamics Restated
  • 15.5 Applications of Thermodynamics: Heat Pumps and Refrigerators
  • 15.6 Entropy and the Second Law of Thermodynamics: Disorder and the Unavailability of Energy
  • 15.7 Statistical Interpretation of Entropy and the Second Law of Thermodynamics: The Underlying Explanation
  • Introduction to Oscillatory Motion and Waves
  • 16.1 Hooke’s Law: Stress and Strain Revisited
  • 16.2 Period and Frequency in Oscillations
  • 16.3 Simple Harmonic Motion: A Special Periodic Motion
  • 16.4 The Simple Pendulum
  • 16.5 Energy and the Simple Harmonic Oscillator
  • 16.6 Uniform Circular Motion and Simple Harmonic Motion
  • 16.7 Damped Harmonic Motion
  • 16.8 Forced Oscillations and Resonance
  • 16.10 Superposition and Interference
  • 16.11 Energy in Waves: Intensity
  • Introduction to the Physics of Hearing
  • 17.2 Speed of Sound, Frequency, and Wavelength
  • 17.3 Sound Intensity and Sound Level
  • 17.4 Doppler Effect and Sonic Booms
  • 17.5 Sound Interference and Resonance: Standing Waves in Air Columns
  • 17.6 Hearing
  • 17.7 Ultrasound
  • Introduction to Electric Charge and Electric Field
  • 18.1 Static Electricity and Charge: Conservation of Charge
  • 18.2 Conductors and Insulators
  • 18.3 Coulomb’s Law
  • 18.4 Electric Field: Concept of a Field Revisited
  • 18.5 Electric Field Lines: Multiple Charges
  • 18.6 Electric Forces in Biology
  • 18.7 Conductors and Electric Fields in Static Equilibrium
  • 18.8 Applications of Electrostatics
  • Introduction to Electric Potential and Electric Energy
  • 19.1 Electric Potential Energy: Potential Difference
  • 19.2 Electric Potential in a Uniform Electric Field
  • 19.3 Electrical Potential Due to a Point Charge
  • 19.4 Equipotential Lines
  • 19.5 Capacitors and Dielectrics
  • 19.6 Capacitors in Series and Parallel
  • 19.7 Energy Stored in Capacitors
  • Introduction to Electric Current, Resistance, and Ohm's Law
  • 20.1 Current
  • 20.2 Ohm’s Law: Resistance and Simple Circuits
  • 20.3 Resistance and Resistivity
  • 20.4 Electric Power and Energy
  • 20.5 Alternating Current versus Direct Current
  • 20.6 Electric Hazards and the Human Body
  • 20.7 Nerve Conduction–Electrocardiograms
  • Introduction to Circuits and DC Instruments
  • 21.1 Resistors in Series and Parallel
  • 21.2 Electromotive Force: Terminal Voltage
  • 21.3 Kirchhoff’s Rules
  • 21.4 DC Voltmeters and Ammeters
  • 21.5 Null Measurements
  • 21.6 DC Circuits Containing Resistors and Capacitors
  • Introduction to Magnetism
  • 22.1 Magnets
  • 22.2 Ferromagnets and Electromagnets
  • 22.3 Magnetic Fields and Magnetic Field Lines
  • 22.4 Magnetic Field Strength: Force on a Moving Charge in a Magnetic Field
  • 22.5 Force on a Moving Charge in a Magnetic Field: Examples and Applications
  • 22.6 The Hall Effect
  • 22.7 Magnetic Force on a Current-Carrying Conductor
  • 22.8 Torque on a Current Loop: Motors and Meters
  • 22.9 Magnetic Fields Produced by Currents: Ampere’s Law
  • 22.10 Magnetic Force between Two Parallel Conductors
  • 22.11 More Applications of Magnetism
  • Introduction to Electromagnetic Induction, AC Circuits and Electrical Technologies
  • 23.1 Induced Emf and Magnetic Flux
  • 23.2 Faraday’s Law of Induction: Lenz’s Law
  • 23.3 Motional Emf
  • 23.4 Eddy Currents and Magnetic Damping
  • 23.5 Electric Generators
  • 23.6 Back Emf
  • 23.7 Transformers
  • 23.8 Electrical Safety: Systems and Devices
  • 23.9 Inductance
  • 23.10 RL Circuits
  • 23.11 Reactance, Inductive and Capacitive
  • 23.12 RLC Series AC Circuits
  • Introduction to Electromagnetic Waves
  • 24.1 Maxwell’s Equations: Electromagnetic Waves Predicted and Observed
  • 24.2 Production of Electromagnetic Waves
  • 24.3 The Electromagnetic Spectrum
  • 24.4 Energy in Electromagnetic Waves
  • Introduction to Geometric Optics
  • 25.1 The Ray Aspect of Light
  • 25.2 The Law of Reflection
  • 25.3 The Law of Refraction
  • 25.4 Total Internal Reflection
  • 25.5 Dispersion: The Rainbow and Prisms
  • 25.6 Image Formation by Lenses
  • 25.7 Image Formation by Mirrors
  • Introduction to Vision and Optical Instruments
  • 26.1 Physics of the Eye
  • 26.2 Vision Correction
  • 26.3 Color and Color Vision
  • 26.4 Microscopes
  • 26.5 Telescopes
  • 26.6 Aberrations
  • Introduction to Wave Optics
  • 27.1 The Wave Aspect of Light: Interference
  • 27.2 Huygens's Principle: Diffraction
  • 27.3 Young’s Double Slit Experiment
  • 27.4 Multiple Slit Diffraction
  • 27.5 Single Slit Diffraction
  • 27.6 Limits of Resolution: The Rayleigh Criterion
  • 27.7 Thin Film Interference
  • 27.8 Polarization
  • 27.9 *Extended Topic* Microscopy Enhanced by the Wave Characteristics of Light
  • Introduction to Special Relativity
  • 28.1 Einstein’s Postulates
  • 28.2 Simultaneity And Time Dilation
  • 28.3 Length Contraction
  • 28.4 Relativistic Addition of Velocities
  • 28.5 Relativistic Momentum
  • 28.6 Relativistic Energy
  • Introduction to Quantum Physics
  • 29.1 Quantization of Energy
  • 29.2 The Photoelectric Effect
  • 29.3 Photon Energies and the Electromagnetic Spectrum
  • 29.4 Photon Momentum
  • 29.5 The Particle-Wave Duality
  • 29.6 The Wave Nature of Matter
  • 29.7 Probability: The Heisenberg Uncertainty Principle
  • 29.8 The Particle-Wave Duality Reviewed
  • Introduction to Atomic Physics
  • 30.1 Discovery of the Atom
  • 30.2 Discovery of the Parts of the Atom: Electrons and Nuclei
  • 30.3 Bohr’s Theory of the Hydrogen Atom
  • 30.4 X Rays: Atomic Origins and Applications
  • 30.5 Applications of Atomic Excitations and De-Excitations
  • 30.6 The Wave Nature of Matter Causes Quantization
  • 30.7 Patterns in Spectra Reveal More Quantization
  • 30.8 Quantum Numbers and Rules
  • 30.9 The Pauli Exclusion Principle
  • Introduction to Radioactivity and Nuclear Physics
  • 31.1 Nuclear Radioactivity
  • 31.2 Radiation Detection and Detectors
  • 31.3 Substructure of the Nucleus
  • 31.4 Nuclear Decay and Conservation Laws
  • 31.5 Half-Life and Activity
  • 31.6 Binding Energy
  • 31.7 Tunneling
  • Introduction to Applications of Nuclear Physics
  • 32.1 Medical Imaging and Diagnostics
  • 32.2 Biological Effects of Ionizing Radiation
  • 32.3 Therapeutic Uses of Ionizing Radiation
  • 32.4 Food Irradiation
  • 32.5 Fusion
  • 32.6 Fission
  • 32.7 Nuclear Weapons
  • Introduction to Particle Physics
  • 33.1 The Yukawa Particle and the Heisenberg Uncertainty Principle Revisited
  • 33.2 The Four Basic Forces
  • 33.3 Accelerators Create Matter from Energy
  • 33.4 Particles, Patterns, and Conservation Laws
  • 33.5 Quarks: Is That All There Is?
  • 33.6 GUTs: The Unification of Forces
  • Introduction to Frontiers of Physics
  • 34.1 Cosmology and Particle Physics
  • 34.2 General Relativity and Quantum Gravity
  • 34.3 Superstrings
  • 34.4 Dark Matter and Closure
  • 34.5 Complexity and Chaos
  • 34.6 High-temperature Superconductors
  • 34.7 Some Questions We Know to Ask
  • A | Atomic Masses
  • B | Selected Radioactive Isotopes
  • C | Useful Information
  • D | Glossary of Key Symbols and Notation

A steam engine and several passenger cars are shown traveling down a train track. The train has some people on board.

Chapter Outline

  • Define the first law of thermodynamics.
  • Describe how conservation of energy relates to the first law of thermodynamics.
  • Identify instances of the first law of thermodynamics working in everyday situations, including biological metabolism.
  • Calculate changes in the internal energy of a system, after accounting for heat transfer and work done.
  • Describe the processes of a simple heat engine.
  • Explain the differences among the simple thermodynamic processes—isobaric, isochoric, isothermal, and adiabatic.
  • Calculate total work done in a cyclical thermodynamic process.
  • State the expressions of the second law of thermodynamics.
  • Calculate the efficiency and carbon dioxide emission of a coal-fired electricity plant, using second law characteristics.
  • Describe and define the Otto cycle.
  • Identify a Carnot cycle.
  • Calculate maximum theoretical efficiency of a nuclear reactor.
  • Explain how dissipative processes affect the ideal Carnot engine.
  • Describe the use of heat engines in heat pumps and refrigerators.
  • Demonstrate how a heat pump works to warm an interior space.
  • Explain the differences between heat pumps and refrigerators.
  • Calculate a heat pump’s coefficient of performance.
  • Define entropy and calculate the increase of entropy in a system with reversible and irreversible processes.
  • Explain the expected fate of the universe in entropic terms.
  • Calculate the increasing disorder of a system.
  • Identify probabilities in entropy.
  • Analyze statistical probabilities in entropic systems.

Heat transfer is energy in transit, and it can be used to do work. It can also be converted to any other form of energy. A car engine, for example, burns fuel for heat transfer into a gas. Work is done by the gas as it exerts a force through a distance, converting its energy into a variety of other forms—into the car’s kinetic or gravitational potential energy; into electrical energy to run the spark plugs, radio, and lights; and back into stored energy in the car’s battery. But most of the heat transfer produced from burning fuel in the engine does not do work on the gas. Rather, the energy is released into the environment, implying that the engine is quite inefficient.

It is often said that modern gasoline engines cannot be made to be significantly more efficient. We hear the same about heat transfer to electrical energy in large power stations, whether they are coal, oil, natural gas, or nuclear powered. Why is that the case? Is the inefficiency caused by design problems that could be solved with better engineering and superior materials? Is it part of some money-making conspiracy by those who sell energy? Actually, the truth is more interesting, and reveals much about the nature of heat transfer.

Basic physical laws govern how heat transfer for doing work takes place and place insurmountable limits onto its efficiency. This chapter will explore these laws as well as many applications and concepts associated with them. These topics are part of thermodynamics —the study of heat transfer and its relationship to doing work.

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Thermodynamics problems and solutions

thermodynamics basic problems

When solving a Physics problem in general and one of Thermodynamics in particular, it is important to  follow a certain order . Get used to being organized when you solve problems, and you will see how it gives good results. It is worth spending a little time on the previous analysis of a problem before you tackle it.

thermodynamics basic problems

The solved thermodynamic problems shown in these pages make use of these three concepts: work ,  heat and  internal energy to a closed system , generally an ideal gas . These three concepts are related through the First Law of Thermodynamics . We will use the so-called Clausius convention to express the first law: the work is done by the thermodynamic system on its surroundings . In addition, the sign convention that we will use is the following one:

Sign convention : 

  • The work done by a gas on its surroundings is positive when it expands. When the gas compresses, the work is negative.
  • The heat absorbed by a system is positive. The heat supplied by a system to its surroundings is negative.

In addition, we will always use the SI units.

When solving a Thermodynamic problem, follow the following steps:

  • Read carefully the Problem Statement..
  • Draw a picture of the physical situation depicted in the problem statement.
  • Write in your notebook the givens in the problem statement.
  • Identify the equations that you will have to use to solve the problem.
  • Be careful with the signs for the heat, the work and the internal energy variation.
  • Do not forget to include the units in your results.
  • Review the problem and check that the results you have obtained make sense.

Consult the summary table to see how to calculate the work, the heat exchanged and the change in the internal energy for the four main reversible processes of an ideal gas .

On the following pages you will find solved Thermodynamic problems. Try to do them yourself before looking at the resolution.

  • Calculation of the work done by an ideal gas
  • Application of the First Law of Thermodynamics
  • Reversible cycle with an adiabatic process (ideal gas)
  • Theoretical Diesel cycle
  • Theoretical Otto cycle
  • Entropy change of a thermal reservoir and of the universe (Carnot heat engine)
  • Entropy change in irreversible processes - real refrigerator
  • Joule expansion


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How to Learn Thermodynamics: Basic Concepts and Foundations

Last Updated: August 25, 2021 References

This article was co-authored by wikiHow staff writer, Eric McClure . Eric McClure is an editing fellow at wikiHow where he has been editing, researching, and creating content since 2019. A former educator and poet, his work has appeared in Carcinogenic Poetry, Shot Glass Journal, Prairie Margins, and The Rusty Nail. His digital chapbook, The Internet, was also published in TL;DR Magazine. He was the winner of the Paul Carroll award for outstanding achievement in creative writing in 2014, and he was a featured reader at the Poetry Foundation’s Open Door Reading Series in 2015. Eric holds a BA in English from the University of Illinois at Chicago, and an MEd in secondary education from DePaul University. There are 12 references cited in this article, which can be found at the bottom of the page. This article has been viewed 23,112 times. Learn more...

Thermodynamics is the study of relationships between heat and other forms of energy. It’s technically a branch of physics, and it has reputation as one of the most difficult subjects for university students. While it’s true that thermodynamics can be pretty confusing, there’s no reason you can’t succeed if you’re a diligent student! With a little hard work and a razor-sharp focus in class, you’ll be on the right track to mastering this interesting subject.

Is thermodynamics hard to learn?

It is fairly difficult for a lot of people, but by no means impossible.

  • There are also many students out there who find thermodynamics easy compared to fluid dynamics, organic chemistry, or calculus. Difficulty is relative, so if you have a strong background in science and math, there’s no reason to assume thermodynamics will be especially challenging.
  • Many students find the definitions themselves kind of hard to follow. For example, internal energy and internal heat seem like they’d be the same thing, but they’re actually two totally different things. [2] X Research source

How can I learn thermodynamics easily?

Take algebra, differential equations, and physics first.

  • Remember, even if you don’t think you’re ready, the class will be much easier for you if you’re focused and attend every lecture! [5] X Research source
  • A lot of universities require you to take physics, differential equations, algebra, and organic chemistry before you’re allowed to take thermodynamics. [6] X Research source

What is the first law of thermodynamics?

The first law basically says that energy cannot be created or destroyed.

  • There’s actually a law that comes before the first law (the first law was discovered first). It’s known as the “zeroth” law. It states that when two objects are in thermodynamic equilibrium with a third object, then the two objects are also in equilibrium with one another. [8] X Research source

What is the second law of thermodynamics?

The second law deals with entropy and the movement of heat.

  • Entropy is a key concept in thermodynamics. Basically, entropy refers to the amount of energy that's unavailable to do work. A lot of concepts in thermodynamics rely on an understanding of entropy. You’ll learn a lot about this early on in class.

What is the third law of thermodynamics?

The third law states that a pure crystal with no heat has no entropy.

  • Just think of the third law like this: heat has a tendency to leave if a system isn’t closed. If there’s no heat, there’s no transfer. It seems kind of obvious, but it’s an essential law when it comes to the behavior of heat and entropy.

What are the basic concepts of thermodynamics?

You’ll learn a lot about energy, mass, and heat.

  • Any decent thermodynamics professor will cover the key concepts before they get into the relevant math. Be a diligent note taker in class and ask questions when your teacher is covering the concepts and you’ll be fine!

What is the importance of thermodynamics?

Thermodynamics is essential if you want to understand energy.

  • Even if you don’t plan on working in a field related to thermodynamics, you can see the principles everywhere. Thermodynamics are why your appliances work when you plug them into the wall, and why 70 °F (21 °C) water feels cold on your skin, but air of the same temperature is comfortable!

Expert Q&A

You might also like.

Make a Faraday Cage

  • ↑ https://par.nsf.gov/servlets/purl/10018819
  • ↑ https://www.researchgate.net/publication/226002663_Difficulties_in_Learning_Thermodynamic_Concepts_Are_They_Linked_to_the_Historical_Development_of_this_Field
  • ↑ https://www.me.gatech.edu/files/ug/me3322.pdf
  • ↑ https://www.tulane.edu/~sanelson/eens212/thermodynamics&metamorphism.htm
  • ↑ https://www.grc.nasa.gov/www/k-12/airplane/thermo1.html
  • ↑ https://www.grc.nasa.gov/www/k-12/airplane/thermo0.html
  • ↑ http://galileo.phys.virginia.edu/classes/152.mf1i.spring02/LawsThermo.htm
  • ↑ http://labman.phys.utk.edu/phys136core/modules/m3/entropy.html#:~:text=When%20a%20small%20amount%20of,units%20of%20Joules%20per%20Kelvin
  • ↑ https://www.livescience.com/50776-thermodynamics.html
  • ↑ https://www.sciencedirect.com/topics/chemistry/third-law-of-thermodynamics
  • ↑ https://www.sfu.ca/~mbahrami/ENSC%20388/Notes/Intro%20and%20Basic%20Concepts.pdf
  • ↑ http://blog.yalebooks.com/2019/04/24/thermodynamics-in-our-daily-lives/

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Thermodynamics Example Problems

  • Some textbooks do not have enough example problems to help students learn how to solve problems.
  • In other books, the examples do not teach the students the underlying method or approach to solving probelms.
  • In many courses, the instructor posts copies of pages from the solution manual.
  • Often the solution manual does little more than show the quickest way to obtain the answer and says nothing about WHY each step is taken or HOW the author knew which step to take next.
  • Here you will find a hefty number of example problems worked out in great detail.
  • I like to focus on HOW we know which step comes next and WHY certain equations or techniques apply.
  • I hope you learn quickly and easily from these problems.

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The University of Oklahoma catalogue describes AME 2213 this way: “First and second law of thermodynamics are developed and applied to the solutions of problems from a variety of engineering fields. Extensive use is made of differential calculus to interrelate thermodynamics functions” . My interpretation of this description is more specific. Thermodynamics, generally speaking, is the science of energy. The transformation of energy from one form to another, and in many cases thermodynamics is about transforming heat into work, such as in an automobile engine or at a power plant.

The application of Thermodynamics is almost everywhere in our daily life. Examples of some application areas of this subject are: Propulsion, Internal Combustion Engines, Power Plants, Refrigeration and Air Conditioning, Solar Heating, Interaction of Human Body with Surroundings, Biomedical devices, Human body, animal, plants, Ecological systems, etc. In this course on thermodynamics we will focus on the analysis of energy systems and the application of these systems to real world contexts.

There are two approaches of teaching Thermodynamics – microscopic and macroscopic. Classical Thermodynamics (macroscopic approach) does not require detailed knowledge of molecular motion to describe a System . We will mainly use this approach in AME 2213. Statistical Thermodynamics (macroscopic approach) considers quantum mechanical description of molecules. We will occasionally use this approach to improve our basic understanding.


Thermodynamics and Energy

Thermodynamics is the science of energy, including energy storage and energy in transit. The Conservation of Energy Principle states that energy cannot be created or destroyed, but can only change its form. The three forms of energy storage of greatest interest to us are Potential Energy ( PE ), Kinetic Energy ( KE ), and Internal Energy ( U ), which we introduce below. The two forms of energy in transit that we consider are Work ( W ) and Heat ( Q ), and the interactions between these various forms of energy are defined in terms of the First Law of Thermodynamics.

Force and Work

Newton’s Second Law states:


where: F is the force in Newtons [N]

m is the mass in kilograms [kg]


Unity Conservation Ratio:

\[\frac{N\times s^2}{kg\times m}=1\,\,\,\,\,\text{and}\,\,\,\,\,\frac{lbf\times s^2}{32.174,lbm\times ft}=1\]

We now consider the work done (W), the energy in transit requiring both the applied force (F) and movement (x). If the force (F) is constant over the distance moved (x) then the work done is given by:

\[W[J]=F\times x[Nm]\]

where: W is the work done in Joules [J]

F is the force in Newtons [N]

x is the distance moved in meters [m]

However, in general the force (F) is not constant over the distance x, thus we need to sum all the incremental work processes taking into consideration the variation of the force (F). This leads to the equivalent integral form for determining work done (W) as follows:

\[W[J]=\int F\,dx\]

SI and English Units

g \approx 9.81\left[\frac{\si\m}{\si\s^2}\right]\approx 32.2\left[\frac{\si{ft}}{\si\s^2}\right] \implies 1\left[\si\m \right]=3.28 \left[\si{ft}\right]

Mass, Volume

1[\si\kg] \approx 2.2[\si{lbm}]

more correctly:

1 \ [\si{kJ}] = 1.055 \ [\si{BTU}]

  • What is the accuracy of this conversion?

We find that with the above survival kit we can determine many unit conversions between SI & English units, typically as demonstrated in the following block:


Forms of Energy

\[W=\int_{h_1}^{h_2}F\,dx=\int_{h_1}^{h_2}m\times g\,dx=m\times g(h_2-h_1)=m\times\Delta pe=\Delta PE\]

Cooking with Potential Energy

In order to gain an intuitive appreciation for the relative magnitudes of the different forms of energy we consider the (tongue-in-cheek) example of an attempt to cook a turkey by potential energy. The turkey is brought to the top of a 100 m building (about 30 stories) and then dropped from the ledge. The potential energy is thus converted into kinetic energy, and finally on impact the kinetic energy is converted into internal energy. The increase in internal energy is represented by an increase in temperature, and hopefully, if this experiment is repeated enough times the temperature increase will allow the turkey to cook. This remarkable experiment was first reported by R.C.Gimmi and Gloria J Browne – “ Cooking with Potential Energy “, published in the Journal of Irreproducible Results (Vol. 33, 1987, pp 21-22).


Potential Energy

W=\int_0^h F \ \mathrm{d}x = \int_0^h m g \ \mathrm{d}x

Internal Energy

\color{red}\boxed{\color{black}Q=m \cdot C \cdot \Delta T = \Delta U}

What a disappointment! At 0.33°C per fall it will require repeating the experiment 600 times just to reach the cooking temperature of 200°C.

Thermodynamics Systems

For purposes of analysis we consider two types of Thermodynamic Systems:


Properties of a System

The closed system shown above can be defined by its various Properties, such as its pressure (P), temperature (T), volume (V) and mass (m). We will introduce and define the various properties of thermodynamic interest as needed in context. Furthermore the properties can be either Extensive or Intensive (or Specific). An extensive property is one whose value depends on the mass of the system, as opposed to an intensive property (such as pressure or temperature) which is independent of the system mass. A specific property is an intensive property which has been obtained by dividing the extensive property by the mass of the system. Two examples follow – notice that specific properties will always have kilograms (kg) in the units’ denominator.


State and Equilibrium

The State of a system is defined by the values of the various intensive properties of the system.

The State Postulate states that if two independent intensive property values are defined, then all the other intensive property values (and thus the state of the system) are also defined. This can significantly simplify the graphical representation of a system, since only two-dimensional plots are required. Note that pressure and temperature are not necessarily independent properties, thus a boiling liquid will change its state from liquid to vapor at a constant temperature and pressure.

We assume that throughout the system Equilibrium conditions prevail, thus there are no temperature or pressure gradients or transient effects. At any instant the entire system is under chemical and phase equilibrium.

Process and Cycle

A Process is a change of state of a system from an initial to a final state due to an energy interaction (work or heat) with its surroundings. For example in the following diagram the system has undergone a compression process in the piston-cylinder device.


The Process Path defines the type of process undergone. Typical process paths are:

  • Isothermal (constant temperature process)
  • Isochoric or Isometric (constant volume process)
  • Isobaric (constant pressure process)
  • Adiabatic (no heat flow to or from the system during the process)

We assume that all processes are Quasi-Static in that equilibrium is attained after each incremental step of the process.

A system undergoes a Cycle when it goes through a sequence of processes that leads the system back to its original state.

The basic unit of pressure is the Pascal [Pa], however practical units are kilopascal [kPa], bar [100 kPa] or atm (atmosphere) [101.32 kPa]. The Gage (or Vacuum) pressure is related to the Absolute pressure as shown in the diagram below:


The basic method of measuring pressure is by means of a Manometer, as shown below:


The atmospheric pressure is measured by means of a Mercury Barometer as follows:


Solved Problem 1.1 – Using a Barometer to determine the Height of a Building.

\rho_{\text{Hg}} = 13,600 \frac{kg}{m^3}

The approach to solution is illustrated in the following diagram. A free-body force diagram on the column of air allows us to determine the height as a function of the pressure difference ΔP from top to bottom.


Well, exactly 100m? – obviously this is a contrived example. When we first evaluated the height we came up with the result:


In Engineering Thermodynamics we normally present results to within 3 or 4 significant digits. The question that one really should ask is “Is this a reasonable method to measure the height of a building?” and the answer is a resounding NO! In the following we do an uncertainty analysis and find that unless we also measure the air temperature during this experiment (why? temperature doesn’t even appear in the above equations!) then this method has an accuracy of:


Unacceptable by any standards.

Problem 1.2 – Using two manometers to measure pressure drop and downstream pressure of compressed air flowing in a pipe.

A Throttling Valve is often used to control the downstream pressure of a high pressure fluid (such as steam or air) flowing in a pipe. In the following diagram we have a water manometer to measure the pressure drop ΔP caused by the throttling valve as well as a mercury manometer to measure the downstream pressure of the air.



Temperature is a measure of molecular activity, and a temperature difference between two bodies in contact (for example the immediate surroundings and the system) is the driving force leading to heat transfer between them.

Both the Fahrenheit and the Celsius scales are in common usage in the US, hence it is important to be able to convert between them. Furthermore we will find that in some cases we require the Absolute (Rankine and Kelvin) temperature scales (for example when using the Ideal Gas Equation of State), thus we find it convenient to plot all four scales as follows:


Notice from the plot that -40°C equals -40°F, leading to convenient formulas for converting between the two scales as follows:

\[ \color{red}\boxed{\color{black}^{\circ}\text{C} = \frac{5}{9}(^{\circ}\text{F}+40)-40} \ \ \ \ \boxed{\color{black}^{\circ}\text{F} = \frac{9}{5}(^{\circ}\text{C}+40)-40} \]

The temperature in Chicago in winter can be as low as 14°F. What is the temperature in °C, K, and °R. [-10°C, 263 K, 474°R] Note that by convention 263 K is read “263 Kelvin,” and not “263 degrees Kelvin”.

Thermodynamics Copyright © by Diana Bairaktarova (Adapted from Engineering Thermodynamics - A Graphical Approach by Israel Urieli and Licensed CC BY NC-SA 3.0) is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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An Overview of Thermodynamics

The Physics of Heat

  • Thermodynamics
  • Physics Laws, Concepts, and Principles
  • Quantum Physics
  • Important Physicists
  • Cosmology & Astrophysics
  • Weather & Climate

thermodynamics basic problems

  • M.S., Mathematics Education, Indiana University
  • B.A., Physics, Wabash College

Thermodynamics is the field of physics that deals with the relationship between heat and other properties (such as pressure , density , temperature , etc.) in a substance.

Specifically, thermodynamics focuses largely on how a heat transfer is related to various energy changes within a physical system undergoing a thermodynamic process. Such processes usually result in work  being done by the system and are guided by the laws of thermodynamics .

Basic Concepts of Heat Transfer

Broadly speaking, the heat of a material is understood as a representation of the energy contained within the particles of that material. This is known as the kinetic theory of gases , though the concept applies in varying degrees to solids and liquids as well. The heat from the motion of these particles can transfer into nearby particles, and therefore into other parts of the material or other materials, through a variety of means:

  • Thermal Contact is when two substances can affect each other's temperature.
  • Thermal Equilibrium is when two substances in thermal contact no longer transfer heat.
  • Thermal Expansion takes place when a substance expands in volume as it gains heat. Thermal contraction also exists.
  • Conduction is when heat flows through a heated solid.
  • Convection is when heated particles transfer heat to another substance, such as cooking something in boiling water.
  • Radiation is when heat is transferred through electromagnetic waves, such as from the sun.
  • Insulation is when a low-conducting material is used to prevent heat transfer.

Thermodynamic Processes

A system undergoes a thermodynamic process when there is some sort of energetic change within the system, generally associated with changes in pressure, volume, internal energy (i.e. temperature), or any sort of heat transfer.

There are several specific types of thermodynamic processes that have special properties:

  • Adiabatic process - a process with no heat transfer into or out of the system.
  • Isochoric process - a process with no change in volume, in which case the system does no work.
  • Isobaric process - a process with no change in pressure.
  • Isothermal process - a process with no change in temperature.

States of Matter

A state of matter is a description of the type of physical structure that a material substance manifests, with properties that describe how the material holds together (or doesn't). There are five states of matter , though only the first three of them are usually included in the way we think about states of matter:

  • superfluid (such as a Bose-Einstein Condensate )

Many substances can transition between the gas, liquid, and solid phases of matter, while only a few rare substances are known to be able to enter a superfluid state. Plasma is a distinct state of matter, such as lightning 

  • condensation - gas to liquid
  • freezing - liquid to solid
  • melting - solid to liquid
  • sublimation - solid to gas
  • vaporization - liquid or solid to gas

Heat Capacity

The heat capacity, C , of an object is the ratio of change in heat (energy change, Δ Q , where the Greek symbol Delta, Δ, denotes a change in the quantity) to change in temperature (Δ T ).

C = Δ Q / Δ T

The heat capacity of a substance indicates the ease with which a substance heats up. A good thermal conductor would have a low heat capacity , indicating that a small amount of energy causes a large temperature change. A good thermal insulator would have a large heat capacity, indicating that much energy transfer is needed for a temperature change.

Ideal Gas Equations

There are various ideal gas equations which relate temperature ( T 1 ), pressure ( P 1 ), and volume ( V 1 ). These values after a thermodynamic change are indicated by ( T 2 ), ( P 2 ), and ( V 2 ). For a given amount of a substance, n (measured in moles), the following relationships hold:

Boyle's Law ( T is constant): P 1 V 1 = P 2 V 2 Charles/Gay-Lussac Law ( P is constant): V 1 / T 1 = V 2 / T 2 Ideal Gas Law : P 1 V 1 / T 1 = P 2 V 2 / T 2 = nR

R is the ideal gas constant , R = 8.3145 J/mol*K. For a given amount of matter, therefore, nR is constant, which gives the Ideal Gas Law.

  • Laws of Thermodynamics
  • Zeroeth Law of Thermodynamics - Two systems each in thermal equilibrium with a third system are in thermal equilibrium to each other.
  • First Law of Thermodynamics - The change in the energy of a system is the amount of energy added to the system minus the energy spent doing work.
  • Second Law of Thermodynamics - It is impossible for a process to have as its sole result the transfer of heat from a cooler body to a hotter one.
  • Third Law of Thermodynamics - It is impossible to reduce any system to absolute zero in a finite series of operations. This means that a perfectly efficient heat engine cannot be created.

The Second Law & Entropy

The Second Law of Thermodynamics can be restated to talk about entropy , which is a quantitative measurement of the disorder in a system. The change in heat divided by the absolute temperature is the entropy change of the process. Defined this way, the Second Law can be restated as:

In any closed system, the entropy of the system will either remain constant or increase.

By " closed system " it means that every part of the process is included when calculating the entropy of the system.

More About Thermodynamics

In some ways, treating thermodynamics as a distinct discipline of physics is misleading. Thermodynamics touches on virtually every field of physics, from astrophysics to biophysics, because they all deal in some fashion with the change of energy in a system. Without the ability of a system to use energy within the system to do work — the heart of thermodynamics — there would be nothing for physicists to study.

That having been said, there are some fields use thermodynamics in passing as they go about studying other phenomena, while there are a wide range of fields which focus heavily on the thermodynamics situations involved. Here are some of the sub-fields of thermodynamics:

  • Cryophysics / Cryogenics / Low Temperature Physics - the study of physical properties in low temperature situations, far below temperatures experienced on even the coldest regions of the Earth. An example of this is the study of superfluids.
  • Fluid Dynamics / Fluid Mechanics - the study of the physical properties of "fluids," specifically defined in this case to be liquids and gases.
  • High Pressure Physics - the study of physics in extremely high pressure systems, generally related to fluid dynamics.
  • Meteorology / Weather Physics - the physics of the weather, pressure systems in the atmosphere, etc.
  • Plasma Physics - the study of matter in the plasma state.
  • Introduction to Heat Transfer: How Does Heat Transfer?
  • What Is a Thermodynamic Process?
  • What Is an Isothermal Process in Physics?
  • What Is Entropy and How to Calculate It
  • The Isochoric Process
  • What Is Isobaric Process?
  • What Is Conduction?
  • Thermodynamics: Adiabatic Process
  • Calculate the Change in Entropy From Heat of Reaction
  • A Scientific Way to Define Heat Energy
  • The Different Fields of Physics
  • Phases of Matter and Phase Diagrams
  • Laws of Thermodynamics as Related to Biology
  • Specific Heat Capacity in Chemistry
  • Understanding Calorimetry to Measure Heat Transfer

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  • Physics Concept Questions And Answers

Thermodynamics Questions

Thermodynamics is a branch of science that studies the concepts of heat and temperature and the inter-conversion of heat and other forms of energy. The term thermodynamics was coined in 1749 by William Thomson. Thermodynamics is a macroscopic science that is divided into

chemical thermodynamics, statistical thermodynamics, equilibrium thermodynamics, and classical thermodynamics.

The types of thermodynamic systems are:

  • Open System
  • Closed System
  • Isolated System

When changes in volume, pressure and internal energy occur, a system experiences a thermodynamic process. Thermodynamic processes are the movement of heat energy within or between systems. Factors that take place out of the system and those that impact the system’s behaviour are referred to as a surrounding.

  • Adiabatic Process – no heat transfer occurs in or out of the system.
  • Isochoric Process – no volume change occurs, and this system does not work.
  • Isobaric Process – no pressure change takes place.
  • Isothermal Process – no temperature change takes place.

Enthalpy is the measurement of energy in a thermodynamic system.

Calculation of energy in a thermodynamic system gives enthalpy and its formula is:

The thermodynamic value is dependent on the physical state of a system known as the entropy. The measure of the stored energy in a system is given by the thermodynamic potential.

Internal Energy of the thermodynamics system is given by

U=∫TdS−PdV + ∑iμidNi

Helmholtz free energy: F = U – TS

Enthalpy: H = U + PV

Gibbs Free Energy: G = U + PV – TS

Important Thermodynamics Questions with Answers

1. Helmholtz free energy is given by the formula ______

Answer: d) F = U – TS

Explanation: Helmholtz free energy is given by the formula F = U – TS

2. Entropy is defined in which law of thermodynamics?

Answer: c) Second

Explanation: Entropy is defined in the second law of thermodynamics.

3. Match the following:

  • Adiabatic Process   i) no volume change takes place
  • Isochoric Process   ii) no pressure change takes place.
  • Isobaric Process   iii) no temperature change takes place.
  • Isothermal Process   iv) no heat transfer takes place.
  • a)-iv b) iii c) ii d) i
  • a)-i b) iv c) ii d) iii
  • a)-iv b) i c) ii d) iii
  • a)-i b) ii c) iii d) iv

Answer: 3) a)-iv b) i c) ii d) iii

4 . Fill in the blanks: _____ coined the term thermodynamics.

Answer: William Thomson

Explanation: The term thermodynamics was coined by William Thomson in 1749.

5 . State true or false: Thermodynamic potentials are quantitative measures of the external energies associated with the system.

Answer: b) FALSE

Explanation: Thermodynamic potentials are quantitative measures of the stored energy in a system.

6. The entropy of a system approaches a constant value as the temperature ______

  • Approaches absolute zero
  • None of the options

Answer: c) Approaches absolute zero.

Explanation: According to the third law of thermodynamics, the constant value is approached by the system when the temperature approaches absolute zero.

7 . What are the branches of thermodynamics?

Branches of thermodynamics are:

  • Classical Thermodynamics
  • Statistical Thermodynamics
  • Chemical Thermodynamics
  • Equilibrium Thermodynamics

8 . A thermodynamic system undergoes ______

  • Changes in pressure
  • Changes in volume
  • Changes in internal energy
  • All the above options

Answer: d) All the above options.

Explanation: A thermodynamic system undergoes changes in pressure, volume, and internal energy.

9 . The measurement of energy in a thermodynamic system is referred to as ______

  • Equilibrium

Answer: a) Enthalpy

Explanation: Enthalpy is the measurement of energy in a thermodynamic system.

10. Internal Energy of the thermodynamics system is given by the formula ______

  • U=∫TdS−PdV-∑iμidNi
  • U=∫TdS−PdV+∑iμidNi
  • U=∫TdS+PdV+∑iμidNi

Answer: c) U=∫TdS−PdV+∑iμidNi

Practice Questions

  • Define thermodynamics.
  • What are the types of thermodynamic systems?
  • Give the formula to find Gibbs free energy.
  • Which law of thermodynamics states that “the entropy of a system approaches a constant value as the temperature approaches absolute zero”?.
  • The process where no heat transfer in or out of the system occurs is known as ______
  • Adiabatic Process
  • Isochoric Process
  • Isobaric Process
  • Isothermal Process

Watch the video below to understand thermodynamic devices in detail.

thermodynamics basic problems

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Thermodynamics – problems and solutions

The first law of thermodynamics

1. Based on graph P-V below, what is the ratio of the work done by the gas in the process I, to the work done by the gas in the process II?

Thermodynamics – problems and solutions 1

Process 1 :

Pressure (P) = 20 N/m 2

Initial volume (V 1 ) = 10 liter = 10 dm 3 = 10 x 10 -3 m 3

Final volume (V 2 ) = 40 liter = 40 dm 3 = 40 x 10 -3 m 3

Process 2 :

Process (P) = 15 N/m 2

Initial volume (V 1 ) = 20 liter = 20 dm 3 = 20 x 10 -3 m 3

Final volume (V 2 ) = 60 liter = 60 dm 3 = 60 x 10 -3 m 3

Wanted : The ratio of the work done by gas

The work done by gas in the process I :

W = P ΔV = P (V 2 –V 1 ) = (20)(40-10)(10 -3 m 3 ) = (20)(30)(10 -3 m 3 ) = (600)(10 -3 m 3 ) = 0.6 m 3

The work done by gas in the process II :

W = P ΔV = P (V 2 –V 1 ) = (15)(60-20)(10 -3 m 3 ) = (15)(40)(10 -3 m 3 ) = (600)(10 -3 m 3 ) = 0.6 m 3

The ratio of the work done by gas in the process I and the process II :

0.6 m 3 : 0.6 m 3

Based on the graph below, what is the work done by helium gas in the process AB?

Thermodynamics – problems and solutions 2

Pressure (P) = 2 x 10 5 N/m 2 = 2 x 10 5 Pascal

Initial volume (V 1 ) = 5 cm 3 = 5 x 10 -6 m 3

Final volume (V 2 ) = 15 cm 3 = 15 x 10 -6 m 3

Wanted : Work done by gas in process AB

W = P (V 2 – V 1 )

W = (2 x 10 5 )(15 x 10 -6 – 5 x 10 -6 )

W = (2 x 10 5 )(10 x 10 -6 ) = (2 x 10 5 )(1 x 10 -5 )

W = 2 Joule

Based on the graph below, what is the work done in process a-b?

Thermodynamics – problems and solutions 3

Initial pressure (P 1 ) = 4 Pa = 4 N/m 2

Final pressure (P 2 ) = 6 Pa = 6 N/m 2

Initial volume (V 1 ) = 2 m 3

Final volume (V 2 ) = 4 m 3

Wanted : work done I process a-b

Work done by gas = area under curve a-b

W = area of triangle + area of rectangle

W = ½ (6-4)(4-2) + 4(4-2)

W = ½ (2)(2) + 4(2)

W = 10 Joule

4. Based on graph below, what is the work done in process A-B-C-A.

Thermodynamics – problems and solutions 4

W = ½ (20-10)(6 x 10 5 – 2 x 10 5 )

W = ½ (10)(4 x 10 5 )

W = (5)(4 x 10 5 )

W = 20 x 10 5

W = 2 x 10 6 Joule

Heat engine

5. An engine absorbs 2000 Joule of heat at a high temperature and exhausted 1200 Joule of heat at a low temperature. What is the efficiency of the engine?

Heat input (Q H ) = 2000 Joule

Heat output (Q L ) = 1200 Joule

Work done by engine (W) = 2000 – 1200 = 800 Joule

Wanted : efficiency (e)

e = W / Q H

e = 800/2000

e = 0.4 x 100%

Carnot engine

6. An engine absorbs heat at 960 Kelvin and the engine discharges heat at 576 Kelvin. What is the efficiency of the engine.

High temperature (T H ) = 960 K

Low temperature (T L ) = 576 K

Wanted: efficiency (e)

Thermodynamics – problems and solutions 5

Efficiency of Carnot engine = 0.4 x 100% = 40%

7. Based on the graph below, work done by the engine is 6000 Joule. What is the heat discharged by engine each circle?

Thermodynamics – problems and solutions 6

Work (W) = 6000 Joule

High temperature (T H ) = 800 Kelvin

Low temperature (T L ) = 300 Kelvin

Wanted: heat discharged by the engine

Carnot (ideal) efficiency :

Thermodynamics – problems and solutions 7

Heat absorbed by Carnot engine :

6000 = (0.625) Q 1

Q 1 = 6000 / 0.625

Heat discharged by Carnot engine :

Q 2 = Q 1 – W

Q 2 = 9600 – 6000

Q 2 = 3600 Joule

8. The efficiency of a Carnot engine is 40%. If heat absorbed at 727°C then what is the low temperature.

Efficiency (e) = 40% = 40/100 = 0.4

High temperature (T H ) = 727 o C + 273 = 1000 K

Wanted : Low temperature

Thermodynamics – problems and solutions 8

T L = 600 Kelvin – 273 = 327 o C

9. Based on graph below, if the engine absorbs 800 J of heat, what is the work done by the engine.

Thermodynamics – problems and solutions 9

High temperature (T H ) = 600 Kelvin

Low temperature (T L ) = 250 Kelvin

Heat input (Q 1 ) = 800 Joule

Wanted: Work (W)

The efficiency of Carnot engine :

Thermodynamics – problems and solutions 10

Work was done by the engine :

W = (7/12)(800 Joule)

W = 466.7 Joule

10. The high temperature of a Carnot engine is 600 K. If the engine absorbs 600 J of heat and the low temperature is 400 K, what is the work done by the engine.

Low temperature (T L ) = 400 K

High temperature (T H ) = 600 K

Heat input (Q 1 ) = 600 Joule

Wanted: Work was done by Carnot engine (W)

The efficiency of the Carnot engine :

Thermodynamics – problems and solutions 11

Work was done by Carnot engine :

W = (1/3)(600) = 200 Joule

  • What is the primary focus of thermodynamics? Answer : Thermodynamics focuses on the study of energy, its transformations, and its relationship with matter, especially in systems at equilibrium.
  • How is the zeroth law of thermodynamics related to temperature? Answer : The zeroth law states that if two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other. This implies the existence of a property called temperature, which is the same for all systems in thermal equilibrium.
  • What does the first law of thermodynamics describe? Answer : The first law, also known as the law of energy conservation, states that energy cannot be created or destroyed, only converted from one form to another. In a closed system, the change in internal energy is equal to the heat added to the system minus the work done by the system on its surroundings.
  • Why is the second law of thermodynamics crucial for understanding the direction of natural processes? Answer : The second law states that the entropy (or disorder) of an isolated system always increases or remains constant. This dictates that energy spontaneously disperses if not hindered from doing so, providing a direction to natural processes and essentially explaining why certain processes occur spontaneously while others do not.
  • What is entropy, and how does it relate to disorder in a system? Answer : Entropy is a measure of the amount of energy in a system that is unavailable to do work. It is also often described as a measure of the system’s disorder or randomness. In general, higher entropy corresponds to greater disorder or randomness.
  • How does the third law of thermodynamics describe the entropy of a perfect crystal at absolute zero? Answer : The third law states that the entropy of a perfect crystal is exactly zero at absolute zero temperature (0 Kelvin). This means that at this temperature, the system is perfectly ordered.
  • Why can’t heat flow from a colder body to a hotter body on its own? Answer : This behavior is a consequence of the second law of thermodynamics. If heat were to flow from a colder body to a hotter one spontaneously, it would lead to a decrease in the overall entropy of the system, which is not favored by natural processes.
  • What is the difference between an isolated, closed, and open system in thermodynamics? Answer : An isolated system does not exchange energy or matter with its surroundings. A closed system can exchange energy but not matter with its surroundings. An open system can exchange both energy and matter with its surroundings.
  • How is the concept of “work” in thermodynamics different from the everyday use of the term? Answer : In thermodynamics, “work” refers to the process of energy transfer where forces applied to an object move it in a direction parallel to the force. For example, when a gas expands against a piston, it does work on the piston. This is a more specific definition compared to the everyday use of “work,” which might simply mean any task or activity.

What is a Carnot cycle, and why is it significant in thermodynamics? Answer : The Carnot cycle is an idealized thermodynamic cycle that provides an upper limit on the efficiency that any classical thermodynamic engine can achieve during the conversion of heat into work (or vice versa). It’s significant because it sets a fundamental efficiency limit based on the temperatures of the heat reservoirs between which an engine operates.

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Developers spend a lot of time on mundane, repetitive tasks — and surprisingly little on actual coding.

In Stack Overflow’s 2022 developer survey, 63% of respondents said that they devote more than 30 minutes a day searching for answers or solutions to problems — which adds up to between 333 to 651 hours of time lost per week across a team of 50 developers. A separate poll from Propeller Insights and Rollbar found that over a third of developers spend around a quarter of their time fixing bugs, with slightly more than a quarter (26%) setting aside up to half their time fixing bugs.

The trend frustrated William Zeng and Kevin Lu. So earlier this year, they — both veterans of Roblox, the video-game-turned-social-network — created a platform called Sweep to autonomously handle dev tasks like high-level debugging.

“We started Sweep after working at Roblox together and constantly dealing with software chores we knew could be automated with AI,” Zeng, Sweep’s CEO, told TechCrunch in an email interview. “Sweep is like an AI-powered junior dev for software teams.”

TechCrunch previously covered Sweep during Y Combinator’s Summer 2023 Demo Day. But since then, the startup has closed a new financing round, raising $2 million from Goat Capital, Replit CEO Amjad Masad, Replit VP of AI Michele Catasta and Exceptional Capital at a $25 million post-money valuation.

Sweep allows devs to describe a request in natural language — for example, “add debug logs to my data pipeline” — outside of an IDE and generate the corresponding code. The platform can then push that code to the appropriate codebase via a pull request, and address comments made on the pull request either from code maintainers or owners — a bit like GitHub Copilot , but more autonomous.

“Sweep allows engineers to ship faster,” Zeng said. “We’ll handle tech debt accumulated with every code change, such as improving error logs and adding unit tests in addition to refactoring inefficient code.”

Sweep, which specializes in writing Python code, leverages a combination of AI models for code generation. They include OpenAI’s GPT-4 , but also a custom “code search engine” — importantly  not trained on Sweep customer data, Zeng says — that helps plan and execute “repository-wide” code changes.

“We built our own code search engine for Python, which leverages lexical and vector search techniques,” Zeng added. Lexical search looks for literal matches — or slight variations on — portions of code, while vector search can find more loosely related code that shares certain characteristics. “We have one of the best unit test generation abilities available and will run and execute tests in real time,” he continued.

In the future, Sweep plans to beef up its platform’s code generation capabilities with StarCoder , the open source code-generating model from Hugging Face and ServiceNow.

Given AI’s tendency to make mistakes, though, I’m a little skeptical of Sweep’s reliability over the long run. A Stanford-affiliated research team  found that engineers who use AI tools are more likely to cause security vulnerabilities in their apps because the tools often generate code that appears to be superficially correct but poses security issues.

There’s also the copyright question. Some code-generating models — not necessarily StarCoder or Sweep’s own, but others — are trained on copyrighted or code under a restrictive license, and these models can regurgitate this code when prompted in a certain way. Legal experts have argued that these tools could put companies at risk if they were to unwittingly incorporate copyrighted suggestions from the tools into their production software.

Sweep’s solution is prompting users to review and edit any generated code themselves before pushing changes to the target master codebase.

“The main challenges affecting AI developer tools are around reliability and managing large codebases,” Zeng said. “We’re using our knowledge around both older and newer methods to make Sweep robust.”

Sweep charges a pretty penny for its services — $480 per seat per month. (By contrast, the business-focused tiers for GitHub Copilot and Amazon CodeWhisperer cost around $20 per user per month.) But that hasn’t dissuaded customers apparently. Zeng claims that Sweep, with a rather humble war chest totaling $2.8 million, has enough capital coming in from clientele to “last the company years.”

“The new money will be for expanding our team in the coming year from two employees to five,” he continued. “We’re going to continue focusing on Python, and improving across all areas of tech debt from unit testing, refactoring and handling leftover to-dos in the code.”


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