• William Thomson today can be recognized as the best type of engineer and a true man of science as well. One can say for him that he stands in the world’s greatest physicists roll call of honor.
• Sir William’s interest in science was not confined to electricity, magnetism, thermodynamics, and hydrodynamics, but also to geographical questions about tides, the shape of the Earth, atmospheric electricity, and thermal studies.
• He served as professor for 53 years at the University of Glasgow. He became the president of the Royal Society in 1895.
• As a mathematician and physicist, Kelvin laid the foundation theory of electric oscillations. He introduced the absolute scale of temperature and propounded the doctrine of the dissipation of energy.
• As an engineer he was successful in laying the Atlantic cable. The course of his professional work was changed due to his involvement in a controversy over the feasibility of laying a transatlantic cable. While he began work on his project in 1854, he was asked to explain his theories.
• In his reply, William referred to his earlier paper, "On the Uniform Motion of Heat in Homogeneous Solid Bodies and its Connection with the Mathematical Theory of Electricity."
• In spite of all his great achievements and vast knowledge, and number of honors he received from the government William Kelvin remained the simplest, kindest and the most easily approachable man.
• He always encouraged or praised even the humblest student and even would as much care over the simplest thesis that was submitted to him. William taught and put into practice that, "the best performance of everyday occupations of mankind are those to which the principles of science are rigidly applied." Thus his kind of work is given the term, ‘applied science.’
EARLY YEARS
Being a bright and intelligent child, and later to maintain the same levels of intelligence coupled with actual output in Scientific terms, is indeed a rarity. But with William Thomson, who was born on June 26, 1824 in Belfast, Ireland, it was all the more true.
His father James Thomson was a textbook writer and also taught mathematics in Belfast. When William was eight years old, his father received a lucrative offer from the mathematical department of the Glasgow University. He at once accepted this offer and settled down with his flock in the land of his ancestors. He taught his eight children mathematics, most of which was not part of the British University curriculum of that time. There was an unusually close relationship between a dominant father and William, a submissive son, which led to an extraordinary intellectual development of William’s mind.
William’s mother was the daughter of a Glasgow merchant. She died when he was just six years old. The fact should be considered that the Thomsons originally emigrated from Scotland to escape the religious persecution of the Covenant times. There was notwithstanding the Irish birthplace, the pure blood and indomitable spirit of the Scottish Chiefs in his veins and wherewithal, the proverbial seriousness of outlook and sternness, which characterized the typical Scotsman in him.
William at 10 and his brother James at 11 matriculated from the University of Glasgow. At the age of 12, William translated from Latin into English Lucian’s Dialogues of the Gods.
Mrs. Elizabeth King, William Thomson’s sister has described in her book, ‘Lord Kelvin’s Early Home’, an event about his genius. William used to solve mathematical problems even before he was ten. William would try to solve some of those problems, which his father would have set for his class at the university. One day, a particularly difficult problem was given to him. William as usual applied his child brain to solve it and till bedtime couldn’t find a solution to it. A little later when his father was about to sleep, he heard a small voice from upstairs, "Eureka! Eureka!"
His father rushed up to see what had happened. To his surprise, he found his little son, bare-footed in his nightgown on the landing triumphantly holding a slate in scanty light of the stair-gas, on which he had scribbled the solution of the problem.
After his matriculation, William was introduced to the advanced and controversial thinking of Jean - Baptiste – Joseph Fourier, by one of his professors who loaned him Fourier’s path-breaking book, The Analytical Theory of Heat. Regarding the book, he later wrote, "I took Fourier out of the University library and in a fortnight I had mastered it." He wrote a paper ‘Fourier expansions of functions in trigonometrical series’ to defend Fourier’s mathematics against criticism. He showed how Fourier’s mathematics could be applied to other physical phenomena other than heat flow, where it was originally applied.
At 15, he wrote an essay, "An Essay on the Figure of Earth," for which he was awarded. His father advised him, "If you are going in for natural philosophy my son, you must go to Cambridge." Therefore, he entered Cambridge and four years later received his B. A. degree with honors. He came out at the top of the Cambridge Mathematical Tripos list and was designated "The Senior Wrangler." This was an honor, which William Kelvin always aspired. He then assisted the renowned tutor, William Hopkins. Very soon he contributed papers to the Cambridge Mathematical Journal and was praised and discussed everywhere.
Conscious of his health, William always kept himself physically fit by rowing, swimming and taking part in athletics. To keep himself fresh mentally, he took keen interest in music and showed marked talent, to the extent that he was appointed the president of the University Musical Society.
William and his father felt tensed as the date for the Tripos contest drew nearer. For this, the young William had to work hard although he was not much interested in it, as it would be of little help in the career he had marked out for himself. But he wanted the honor as it would greatly help him in securing a position as professor of natural philosophy at Glasgow, a post, which would soon be vacant and which his father (an elderly professor) had set his sights on for his son. Therefore, he ‘crammed as best as he could’ and had high hopes, of attaining top position. But unfortunately when the results were out, he stood second on the list. Parkinson of St. John was the first. Yet, there was another valued mathematical prize, again for which both of them had contested. It was now William’s turn, to receive Smith’s Prize. William then left for Paris to study under the famous Regnault, a physicist (on whose foundation work, entire chapters in theoretical and physical chemistry have been based).
In 1846, the Chair of National Philosophy (Later known as Physics) was vacant. His father planned a spirited campaign on his son’s behalf to secure the esteemed position. William’s father’s wish was finally fulfilled. At the age of 22, William was unanimously elected professor at Glasgow.
In 1852, he married Margaret, daughter of his father’s great friend Walter Crums of Thornliebank. After their engagement, she wrote to her sister, "We have one interest in common that can never fail. I feel that in William’s love for his sisters lies my best security for the continuation to me of those feelings on which the happiness of my life depends." Theirs was a happy married life except that they did not have children.
His wife accompanied him on most of his tours. But her health was always cause for concern. This caused him so much anxiety that he had to ask for leave from Glasgow to take her abroad for recovery. On one of these trips, he met the great German physicist, Hermann von Helmholtz who later became one of his closest friends.
Unfortunately, traveling did not improve Margaret’s health and it deteriorated. Though Margaret had always been ailing, she wrote a number of poems which included translations of German poems. One of their friends wrote about her, "Sincere, bright and very keen-minded, and with a true insight into the real worth of things and thought."
She died in 1870 leaving William heartbroken. This grief cast a shadow over his life, leading to his constant traveling, especially to supervise the laying of the Atlantic cable. During his voyages, he met Madeira, Frances Blandy daughter of a wealthy merchant of Funchal, in 1874. He soon realized that she could be the only person who could get him out of the mourning. Thereafter, they became engaged and got married in the British Consular Chapel. The second marriage gave a new lease of life to William.
In his latter life, William Thomson became a partner in two engineering consulting firms after the successful laying of the trans-Atlantic cable. This played a major role in the planning and construction of submarine cables during the frenzied era of expansion. It again resulted in a global network of telegraph communication. William became a wealthy person, who could afford a 126-ton yacht and a baronial estate.
He retired from Glasgow in 1899. Although he was elected chancellor of the university, he was rarely seen in public, but at the same time he was well acquainted and also followed every new development of science with keen interest and his pen was never idle.
Later his second wife’s health affected him. In 1907, she had a paralytic stroke. He himself caught a chill that developed into a severe bout of sickness. It worsened and he had septic fever. He breathed his last on December 17, 1907, surrounded by friends and those he loved. He was buried at Westminster Abbey, London.
Kelvin felt that in the truism between religion and science there can be no real conflict and he often insisted that he was a "great believer in design".
"Mount where science guides,
Go measure earth weigh air, and state the tides,
Instruct the planets in what orbs to run,
Correct old time regulate the sun."
The above lines aptly describe Sir William Thomson. A Scottish engineer, mathematician and physicist, all rolled into one, had one of the keenest and most versatile minds that answered every call of science. He investigated and studied each branch of physical science. His inventions aided the development of industry and the welfare of his fellowmen. His discoveries and researches are truly remarkable, especially the submarine cable and the improved mariner’s compass.
One of his closest friends Helmholtz had written to Kelvin’s wife about his impression of his great contemporary, "I expected to find the man, who is one of the first mathematical physicists of Europe, somewhat older than myself and was not a little astonished when a juvenile and exceedingly fair youth, who looked quite girlish, came forward….He far exceeds all the great men of science with whom I have made personal acquaintance, in intelligence, lucidity, and nobility of thought, so that I felt quite wooden beside him sometimes."
His was a vast contribution to science. This included development of thermodynamics, the absolute scale, the dynamical theory of heat, mathematical analysis of electricity etc. Moreover, he also invented the mirror galvanometer used as signaling device and the siphon recorder, which is still in use for receiving signals.
June 26, 1824 Born in Belfast, Ireland.
1834 Passed his matriculation examination.
1838 Began University level work.
1841 Entered Cambridge. In the same year his first paper was published.
1844 Received his B. A. degree.
1846 He was elected as professor of natural philosophy at the University of Glasgow.
1847 First defined the absolute temperature scale.
1851 His paper, "On the Dynamical Theory of Heat" was published.
1866 Wrote one of his essays, ‘Great Eastern at Sea’.
1870 Death of his wife Margaret.
June 24, 1874 Second Marriage with Madeira.
1889 Retired from University of Glasgow.
1890 Elected as President of Royal Society.
1904 Elected as chancellor of the University.
December 17, 1907 Died due to septic fever.
William’s scientific work was directed by the conviction that the various theories dealing with matter and energy converged towards one great unified theory. He followed the goal of a unified theory, even though he doubted its attainment in his lifetime. The basis of his conviction was the cumulative impression got from experiments showing the interrelation of forms of energy. That magnetism and electricity, electromagnetism and light are related was proved by 19th century. Whereas, William had shown through mathematical analogy that there was a relationship between hydrodynamic phenomena and an electric current flowing through wires. According to James Prescott Joule, there was relationship between mechanical motion and heat. This idea of his became the very basis for the science of Thermodynamics.
In 1847, William first heard Joule’s theory of the inconvertibility of heat and motion at a meeting of the British Association for the Advancement of Science. Joule’s theory worked as a counter to the accepted knowledge of the time, that heat was an imponderable substance (caloric) and could not be a form of motion. William discussed the implication of his new theory with Joule.
Although William could not accept Joule’s idea at that time, he willingly reserved the judgment, especially because the relation between heat and mechanical motion fitted into his own view of the causes of force. Along with a cautious endorsement in a major mathematical treatise, ‘On the Dynamical Theory of Heat’, William was able to give public recognition to Joule’s theory by 1851.
Actually, William’s work on electricity and magnetism began during his student days at Cambridge. Much later, when James Clark Maxwell decided to undertake research in magnetism and electricity, he read all of William’s papers on that subject and adopted William as his mentor. William contributed many new scientific theories and ideas in the 19th century. He even advanced the ideas of Michael Faraday, Fourier, and others.
William by using mathematical analysis drew generalizations from experimental results. He then formulated the concept, which was to be generalized into the dynamic theory of energy. William also collaborated with scientists like Sir George Gabriel Stokes, Herman Von Helmholtz, Peter Guthrie Tait and Joule. He advanced the frontiers of science in many areas, especially hydronomics. He also developed the mathematical analogy between the flow of heat in solid bodies and the flow of electricity in conductors.
In 1850, an experimental line had been laid down between Dover and Calais, where the cable used was a copper wire, which was insulated by gutta-percha (a hard tough thermoplastic substance) on a trial run. The signals received were characterized as ‘extraordinarily sluggish’, and consequently the communication was ended within two hours. This was due to the line having been severed by the anchor of a fishing smack. This difficulty was overcome by using a thicker cable.
A proper application of the general principle was lacking. In May 1855, William presented a paper ‘On the Theory of the Electric Telegraph’ before the Royal society. According to William, the retardation of electric impulse along a cable was proportional to the capacity and the resistance of the cable. Each of these quantities was proportional to the length to that extent that the time retardation of a signal was in actual practice proportional to the square of length. William illustrated, "If a cable 200 miles long showed a retardation of 1/10th second, one with 2,000 miles of similar thickness would have retardation 100 times as great or ten seconds."
Although there existed many who scoffed and objected, William’s reputation as a practical physicist, his theories and opinion mattered. It helped him plan out the forming of the Atlantic Telegraph Company, as its chief director.
Finally, a cable was successfully laid down but it struggled to register the signals. William’s solution was the invention of the celebrated mirror galvanometer. William attached a spherical mirror to the magnet at the center of the coil of an ordinary galvanometer in a manner that it hung suspended vertically and swung with the magnet whenever a current passed round the coil.
"A spot of light from a lamp was reflected from this mirror on to a distant scale being placed sufficiently far away. A tiny movement on the part of the mirror caused a very noticeable swing of the spot along the scale, and thus proved exceedingly sensitive to even the smallest current changes." By doing so, feeble cable currents received were successfully recorded and it seemed as if the problem was solved. But actually it didn’t as when the tide of rejoicing was at its highest, the messages ceased and unfortunately all efforts to revive the cables failed. This cannot be regarded as complete failure, as 700 messages, some of them of great importance, were recorded.
William was not disappointed. He said, "We must build a new and better cable." Then he became busy in making plans, arranged to have a cable ship. The Great Eastern ship carried the whole length of cable required to equip it for the freedom of maneuvering in the laying operations. Two attempts were made and eventually succeeded in 1866. The original cable was made serviceable. William was honored by the Queen for his success.
One more famous work in the early 1860s, was his joint project with Tait their famous Treatise on Natural Philosophy. They worked through correspondence on this huge project, which William envisaged to cover all his physical theories. They intended to write many volumes, but could complete only the first two : kinematics and dynamics. These were remarkable and served as standard texts for many generations of scientists.
He wrote number of scientific journals and papers, of which ‘Mathematical and Physical Papers’ and ‘Elements of Natural Philosophy’ were very popular.
THERMODYNAMIC SCALE
William’s was a very important contribution towards the making of reliable thermometers, specially a scale of temperatures now universally known as William’s Absolute Thermodynamic Scale. This scale is solely concerned with the work done by the thermometric substance employed. It is totally independent of all its properties. Actually it is the most satisfactory scale of temperatures. The one that can be called into account where the applicability of ordinary thermometers is limited. For instance under certain conditions, the liquid of thermometer may freeze or evaporate or the material of bulb may change its volume or some of gas may be absorbed in the case of gas thermometer. Similarly, mercury thermometer also has its limitation, as it cannot be used accurately above 450ºC and hydrogen thermometer cannot be used above 500ºC. For such high temperatures extraordinary precautions are necessary to secure accuracy.
Kelvin’s accurate thermodynamic scale simplifies all this. Above all the working out of its principles forms one of the ABC’s in the laws of radiation. Kelvin laid down the Laws of Thermodynamics adding a new dimension to the scientific field.
BASIC CONCEPTS OF THERMODYNAMICS
Thermodynamics can be defined as a branch of science that deals with energy in all its forms. The laws govern the transformation of energy like mechanical, thermal or heat, chemical, electrical etc. This science covers a broad field of application and is a base to many branches of natural science, engineering and technology. The part that applies to engineering is usually referred to as ‘Engineering Thermodynamics or Applied Thermodynamics’.
Thermodynamics also deals with the behavior of gases and vapors. It is when matter is subjected to variations of temperature and pressure and the relationship between heat, energy and mechanical energy that the commonly known term work comes into picture. Energy transformation is likely to occur when a substance undergoes a change from one state to another in a process. Common processes include heating, or cooling and expansion, or compression in the cylinder or passages with or without production or supply of mechanical work. Sometimes due to chemical reaction and/or change of phase occurs in some processes involving liberation of heat.
The laws based on experimental results acquired from the study of gases and vapors are useful in designing of boilers, steam engines, steam turbines, internal combustion engines, gas turbines, refrigerating machines and air compressors. The demand for energy is increasing rapidly at present. Therefore it is essential that thermal plants and machines are designed and operated at the peak level of performance for efficient and optimal utilization of fuels and natural resources available.
WORKING SUBSTANCE OR MEDIUM
Any thermodynamic process of change covers the use of working substance or thermodynamic medium that has the ability to receive, store and give out (or reject) energy as required by the particular process. The medium may be in any one of the four physical states or phases – solid, liquid, vapor and gaseous. Sometimes, the vapor and gaseous substances together are termed as gases.
The use of some working medium is required for the power generating machines (plants), which operate as per thermodynamic laws, such as steam power generating plants that use water vapor and refrigerator or ice plants use ammonia or freon gas for their working. Steam is a very suitable medium for steam power plants as it quickly absorbs heat that flows easily, exerting pressure on the piston or blade while it moves and allows considerable expansion of its volume. Whereas Ammonia or Freon is suitable medium for an ice plant as it boils at a temperature below 0ºC and at a moderate pressure, absorbs heat from water and turns it to freeze into ice. A mixture of air and fuel forms a working medium in the initial processes and a product of combustion forms the remaining processes of internal combustion engines and gas turbines.
SYSTEM
A thermodynamic system is ‘a specific portion of matter, with definite boundary on which our attention is focussed.’ It is irrespective of the form of system that is system boundary may be real or imaginary, fixed or deferrable. Everything outside the system that has direct bearing on its behavior is known as ‘surroundings’ as shown in figure given below.
Thermodynamic problems are related with the transfer of energy and mass across the boundary of a system. There are three different types of systems – isolated, closed and open.
An isolated system cannot exchange energy as well as mass with its surroundings. The system and surroundings together form Universe. Therefore Universe is considered as Isolated System.
As far as closed system is concerned, transfer of energy (work and / or heat) takes place whereas transfer of mass does not. The above figure shows the closed system. It includes compression of a gas in a piston cylinder assembly, refrigerator, heating of water in a closed vessel etc.
In an open system, mass and energy both may be transferred between the system and the surroundings. Gas turbine, axial flow and centrifugal air compressors, boiler delivering steam and also the steam turbine are the examples of this system.
STATE AND PROPERTIES OF SUBSTANCE
It is the state and variables that determine the state or properties or parameters that represent the exact condition of a substance. The principal properties are pressure, volume, temperature, internal energy, enthalpy and entropy. But pressure, volume and temperature are its fundamental properties. The other properties listed above are dependent in some manner on one or more of these fundamental properties. Any two of the properties like pressure, volume etc. much to be known to decide the ‘Thermodynamic State’ of a working medium. So if the thermodynamic state is fixed, then all these properties are fixed with it.
PROCESS AND CYCLE
A change of state takes place when one or more of the properties of a system changes. It is said to have undergone a process only when a system undergoes changes of its state. Hence the process is the path joining succession of states passed through by a system. Process is named according to its specification that is constant pressure process and constant volume process etc.
A cycle is defined as process or combination of processes, so conducted that the initial and final states of the system are the same. A thermodynamic cycle is also known as a Cyclic Operation of Processes.
TERMS / PROPERTIES OF THERMODYNAMICS
PRESSURE
Pressure is a force applied over a unit area. The atmosphere surrounding the earth exerts pressure on its surface equivalent to the weight of air over a unit area of the earth’s surface. Barometer records the pressure of the atmosphere.
VACUUM
Vacuum means absence of pressure. Many a time it happens that the pressure confined in fluid is less than that of the surrounding atmosphere. That confined fluid is then said to be under partial vacuum. In such a situation, the instrument used to measure the pressure is vacuum gauge. This instrument records the difference between the surrounding atmospheric pressure and that within the vessel in millimeters of mercury. It is said to have perfect vacuum when a vessel does not have any pressure within it.
VOLUME
Volume is defined as the space, which the gas occupies and it is measured in cubic meters. A widely used unit of volume is the liter, which is 1000th part of a cubic meter that is 1 liter = 10-3 m3.
TEMPERATURE
The temperature of a substance is the measure of hotness or degree of coldness of body. A body is said to be hot when it has relatively high temperature and cold when it has relatively low temperatures. It is commonly known that heat energy has a tendency to flow from a hot body to one which is cooler. This means temperature decides which way or directions the flow of heat will take place.
Instruments called thermometers measure temperature and pyrometers are the instruments to measure very high temperatures. Thermometers and thermocouples measure the small and precise changes of temperature. Engineers measure it by centigrade thermometer.
ENERGY
Energy can be defined as the capacity that a body possesses for doing work. Energy residing in a system is called stored energy. Energy is seen in many forms. They are mechanical (potential and kinetic), internal (or thermal), electrical, chemical and nuclear energy.
Energy in transition is the energy that is transferred to or from a system. The significance of transient form is restricted only up to its transfer. Work and heat are forms of energy in transition that can only cross the boundaries of a system. There is nothing like work of a body or heat of a body as both work and heat is not stored in the system. Work and heat are neither properties nor functions of state. They are only path functions and exist only in transit.
WORK
Work is a transient form of energy. Work is done when a force acts upon a body causing the body to move and to overcome resistance continually. This work is equal to the force multiplied by the distance through which it acts, where time factor is of no consideration.
The unit of a work done is Newton-Meter (N-M), which is product of a unit force (one Newton) and a unit distance (1 meter), moved in the direction of force. This unit of work is also known as joule (J), that is
1 joule = 1 Newton-meter (N-m)
1 kilo joule (kj) = 1,000 joules.
HEAT
Heat is a form of energy, which is transferred from one body to another on account of temperature difference. Therefore, heat energy is not stored form of energy but occurs only in transition. When it is present, energy of some other form is being transferred from one body to another.
Heat energy can be transferred in three ways that is through conduction, convection and radiation. In all the three modes of heat transfer, there must be temperature difference and heat transfer takes place in the direction of decreasing temperature. It is necessary to note that conduction and convection need some definite medium, whereas radiation can occur in vacuum also.
POTENTIAL ENERGY
Potential energy can be defined as the ‘energy of a body due to its position or elevation relative to some plane’. The term potential energy is exclusively used for gravitational energy. The potential energy of a substance is equal to the work, which can be done by allowing a substance to fall from a position down to the surface of the earth. Maximum possible work done is the product of gravitational force or weight of a falling body and also the distance through which this body falls.
This unit of potential energy is Newton-Meter and it is symbolically represented as PE.
KINETIC ENERGY
The Kinetic Energy (KE) possessed by a body is due to its motion. The unit of this energy is also Newton-Meter. For example, water held in a dam has potential energy but when water is released, the potential energy that exists in its flow changes into Kinetic Energy. Hence, the energy could be utilized or work could be done equal to the energy stored in the water by permitting it to flow through gates of the dam or blades of the water turbine.
INTERNAL ENERGY
Matter is composed of an aggregation or collection of molecules, which are moving continuously. The movement of molecules is more pronounced in gases than in liquids. Gas becomes stagnant or does not move at all, when it is stored in closed vessel or system. It possesses a considerable amount of Internal Kinetic Energy because of the motion of its molecules within the closed vessel. Besides the internal kinetic energy, substances have internal potential energy because of the relative position of their molecules with respect to one another.
A change in mechanical potential energy of a body occurs, when the elevation of the body relative to the earth is altered.
The internal energy U of a substance may be defined as the algebraic sum of internal kinetic and the internal potential energy of its molecules. Internal energy is an extensive property since it depends upon the mass of the system.
ENTHALPY
Total heat and heat-content are the other terms used for enthalpy. Enthalpy is an energy term. It is defined as H = U + PV. U is the internal energy, P is the absolute pressure and V is the volume.
ENTROPY
The term entropy means ‘transformation’. It is a thermodynamic property of a working substance that increases with the addition of heat and decreases with the removal of heat. It may be regarded as a thermodynamic variable (parameter of thermodynamic state like pressure, temperature etc.) introduced to facilitate the study of working fluids (working substances), when they are passing through reversible cycle (cycle consisting of only reversible operations). Engineers use it as a means of providing quick solutions to problems dealing with entropic operation. Entropy is usually represented by the symbol p (pai). The small increase of entropy, d p of a substance is defined as the ratio of small addition of heat, dp to the absolute temperature, T of the substance at which the heat is supplied. That is
d p = d p /T or d p = T × d p .
LAWS
Different scientists have formulated different laws. They include Boyle, Charles, Gay-Lussac, Regnault and Joule. Here all these laws are explained in brief.
BOYLE’S LAW
Boyle has experimentally proved/established that when a perfect gas is heated at constant temperature, the volume of a given mass of gas is inversely proportional to the absolute pressure. Therefore volume increases as the absolute pressure decreases and vice versa.
CHARLE’S LAW
This law states that if a perfect gas is heated at constant pressure, its volume varies directly with the absolute temperature. It can be explained in other words as ‘co-efficient of expansion is constant at constant pressure’. That is its change of volume per degree of temperature change is constant. He found that this change in volume would be same for all perfect gases.
GAY-LUSSAC LAW
This law expresses relationship between temperature and pressure of a perfect gas when the volume is kept constant. It can be stated that volume remaining constant, the absolute pressure varies directly as the absolute temperature.
When V (volume) is constant
P µ T P/T = C (a constant)
Finally, it states by applying the above
P1/T1 = P2/T2 or P1/P2 = T1/T2.
REGNAULT’S LAW AND JOULE’S LAW
Regnault’s law says that the specific heat of a perfect gas at constant pressure is constant and its value at constant volume is also constant.
This is expected to hold good for many thermodynamic calculations. A variation in the values of specific heat of constant pressure and constant volume for any gas is found. The value of specific heat may increase to a certain extent with the increase in temperature. However, the law is assumed to hold good within small range of variation of temperature from which it follows that the ratio of the two specific heats kp and kv of any given gas is a constant. Therefore y = kp/kv = constant.
Joule’s law states that the internal energy of a gas is function of the temperature only and is independent of the pressure or volume of the gas. Therefore the internal energy of a gas is proportional to the absolute temperature.
Joule’s experiment was conducted with two insulated pressure vessels, connected by a pipe and a valve. One vessel was at a higher pressure than the other. The valve was opened and the gas was allowed to have free un-resisted expansion. Applying the law of conservation energy,
Q = dU + W
Q = 0 because no heat was supplied or rejected and
W = 0 because no work was done.
dU = 0 i.e. internal energy did not change.
It was found that after free expansion, the temperature did not change. Therefore it was concluded that internal energy of a given mass of gas depends upon its temperature only.
LAW OF THERMODYNAMICS
The element of the thermodynamic approach to the description of the behavior of matter is to take a particular region of space and its contents and to consider the transfer of energy across the boundary, which separates this region from its environment. It is necessary to examine then, the kind of description that can be simply given of an assembly of matter and to determine the laws that govern the transfer of energy across the boundary of that assembly of matter.Laws of Thermodynamics lie at the center of the classical thermodynamics. These laws are : Zeroth Law, First, Second and Third Law. They are natural or fundamental laws formulated on basis of natural observations and not derived from any mathematics.
ZEROTH LAW OF THERMODYNAMICS
When two bodies, one hotter than the other are brought into contact with each other, both the bodies become equally hot after sometime. The two bodies are said to be in thermal equilibrium when this state is attained. The bodies in thermal equilibrium will have some property in common. This property is called Temperature. The temperature indicates the intensity of molecular activities that is kinetic fraction of internal energy. Higher the temperature, greater is the level of activity. When two bodies with different temperatures are brought into contact, an increase will take place in the molecular activities of one of the bodies, which is at the lower temperature and decrease will take place in other body that is at higher temperature. These changes will continue till the temperature of both the bodies are same / equal. Then the bodies will attain thermal equilibrium with each other.
The association of temperature with the qualitative evolution of internal kinetic energy may be extended to the formulation of the Zeroth law of thermodynamics.
Only when the properties of a system are uniform throughout and the external conditions are unaltered, then the system is said to be in thermodynamic equilibrium. When a system is in thermodynamic equilibrium, it satisfies all the three mechanical, thermal and chemical equilibrium that is thermodynamic equilibrium can be attained only when the system is in these three equilibrium.
FIRST LAW OF THERMODYNAMICS
This law is the same as the law of the conservation of energy that energy can neither be created nor destroyed, only if the mass is conserved. The sum of all energy of the universe is constant. Even then energy can be converted from one form to another. This is the thermodynamic aspect of the First Law.
Joule established that heat and mechanical energies are mutually convertible. For the production of the heat, a definite number of units of work for each unit of heat is produced. In the same manner, heat produced by its disappearance, a definite number of units of work for each unit of heat converted, is produced. This is called the first law of thermodynamics.
SECOND LAW OF THERMODYNAMICS
The second law states that it is impossible for self-acting machine, unaided by any external agency to convey heat from a body at low temperature to a body at higher temperature. This means heat cannot itself pass from a cold body to warmer body. This statement proposed by Clausius, is known as the Second Law of Thermodynamics.
According to the second law, heat can be forced to pass to a higher temperature, as in the action of refrigerating machine. It is possible only by applying an ‘external agency’ to derive the machine that is by doing work on the system.
To formulate the second law, a number of statements have been given. They can be expressed logically equivalent to any one statement that can be derived from the other. Like the first law, the second law is also the statement of the net result of common experiences.
Some of the statements given are more or less indicative of one and the same meaning. They are :
"No apparatus can operate in such a way that its only effect (in system and surroundings) is to convert the heat taken in completely into work."
"It is impossible to convert the heat taken in completely into work in a cyclic process."
"For heat to be converted into work, there must be in addition to the source of heat, a cooling agent possessing a lower temperature that is there must be a drop in temperature."
"The heat of the cooler body in the given system cannot serve as a source of work."
"It is impossible to construct an engine that operating in a cycle, will produce an effect other than the extraction of heat from a single reservoir and the performance of an equivalent amount of work" – Kelvin-Planck
• "When you measure what you are speaking about and express it in numbers, you know something about it, but when you cannot express it in numbers your knowledge about is of a meager and unsatisfactory kind."
• "Do not imagine that mathematics is hard and crabbed, and repulsive to common sense. It is merely the etherialization of common sense."
• "I am never content until I have constructed a mechanical model of what I am studying. If I succeed in making one, I understand; otherwise I do not."
• "No cyclic process is possible whose sole result is a flow of heat from a single reservoir and the performance of equivalent work."
• "There is at present in the material world a universal tendency to the dissipation of mechanical energy."
• "Science is bound, by the everlasting vow of honor, to face fearlessly every problem, which can be fairly presented to it."
• "The life and soul of science is its practical application."
• "In science there is only physics; all the rest is stamp collecting."
• "Blow a soap bubble and observe it. You may study it all your life and draw one lesson after another in physics from it."
• "…. Motion is the very essence of what has hither to been called matter."
• "We can conceive that electricity itself is to be understood as not an accident, but an essence of matter. Whatever electricity is, it seems quite certain that electricity in motion is heat, and that a certain alignment of excess of revolution in this motion is magnetism."
• "If you cannot measure it, you cannot improve its."
• "Mathematics is the only good metaphysics."
• "Radio has no future."
• "The steam-engine is passing away."
• "A great reform in geological speculation seems now to have become necessary."
• "Physicists are not wholly incapable of appreciating geological difficulties."
• "It would, I think, be exceedingly rash to assume as probable anything more than 20 million years of the sun’s light in the past history of the earth, or to reckon on more than five or six million years of sunlight for time to come."
• "What would you think of a Universe in which you could travel one, ten, or a thousand miles… and then find it came to end ? Even if you were to go millions and millions of miles, the idea of coming to an end is still incomprehensible."
• "The animal body does not act as a thermodynamic engine…. consciousness teaches every individual that they are, to some extent, subject to the direction of his will. It appears therefore that animated creatures have the power of immediately applying to certain moving particles are directed to produce derived mechanical effects."
• "Do not be afraid of being free thinkers ! If you think strongly enough you will be forced by science to the belief in God, which is the foundation of all religion. You will find science not antagonistic but helpful to religion."
• William Thomson won a prize at the age of 12 for translating from Latin Lucian’s Dialogues of the Gods. He won University gold medal when he was 16 for his essay, ‘On the Figure of the Earth.’ He stood second as senior Wrangler and got the first valued mathematical prize and that was Smith’s Prizeman.
• In 1866 Queen Victoria knighted him and he became Sir William Thomson. He became Baron Kelvin of Largs in 1892. In 1896 the jubilee of his professorship at Glasgow was celebrated, which was unique in the history of the university. In 1902, he received the Order of Merit.
• Thereafter, William Thomson was known as Lord Kelvin.
