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Edit Comment Close Premium member Presentation Transcript History of the Electric Charge: History of the Electric Charge Jana M. Jilek, P. Eng. Red River College July, 2001 ©2001 Slide2: We encounter electricity in various forms countless times every day. Electricity runs the clock radio that wakes us up, it supplies electric lights, toasters, electric trains, T.V.'s, computers, and numerous other devices we use. In its untamed form, electricity crackles in the fur of a cat when we pet it. It is the awesome power in a lightning. Electricity is also behind the displays of northern lights. Slide5: We teach how electricity “works”, how to predict behaviour of electric devices, and how to improve their performance. But do we really understand electricity? This presentation intends to show how our present theories developed and give reasons for some of the inconsistencies in the theories.Slide6: What is electricity? What is electric charge? How does it move? Why does it move? How do we know electric charge exists? The more basic is the question, the more difficult it is to answerThe people of ancient Greece knew that amber that has been rubbed attracts light objects like hair, fur or straw. : The people of ancient Greece knew that amber that has been rubbed attracts light objects like hair, fur or straw. Plato (c. B.C.400) considered this effect similar in nature to the magnetic effects of magnetite. Plutarch (c. A.D.100) believed that the movement of small objects towards the rubbed amber is due to the movement of air around it. He also noticed that there is a difference between the effect of magnetite and that of rubbed amber - magnetite attracts only iron, while amber will cause light objects of different materials to move towards it.Slide8: Plutarch formulated a theory: As an electric is rubbed, there is an effluvium emitted by it. The effluvium displaces the air around the electric, the air moves away from the electric, bounces off the undisturbed air behind it and as the air returns back to the electric it brings along the light objects in its path. Slide9: By the beginning of the 16th century, it was known that there are other materials that display the same effect - diamond, saphire, opal, sealing wax and many more. William Gilbert in his book “De magneta” (1600) introduced a new latin word electrica to refer to the materials that displayed the same effect as amber. Its meaning was “an ability to attract bodies”. Slide10: William Gilbert had an access to the queen Elizabeth I as her royal physician. During Elizabeth’s reign, England had the largest navy in the world. Discovery of the New World and the desire for its economic exploitation made navigation at sea the most pressing scientific problem of this time. Gilbert’s book and experiments explained the working and the irregularities of compass; the electric attraction was only briefly mentioned. In this picture Gilbert shows to the queen the electric attraction of a glass rod. Slide11: William Gilbert tried to explain why the electric attraction exists. The idea of an action at a distance was not acceptable to the philosophers and scientists of his times, therefore he speculated: An electric heats up when rubbed, and the heat releases a material effluvium that joins the electric and the attracted bodies and holds them together. Gilbert invented and used a “versarium” to detect the electric charge: Gilbert invented and used a “versarium” to detect the electric charge Gilbert made large number of experiments to confirm his hypothesis. In the course of his experiments he looked for and found a relationship between the attractive force and the distance between the electric and the attracted objects: the attractive force decreases as the distance increases. This was well explained by his theory - at large distances the effluvium spreads out through the space and becomes thinner.Slide13: We see what we want to see Gilbert did not look for repulsive force and therefore he did not find one. Light objects move towards the electric - therefore Gilbert assumed the force is only in one direction - the electric acts on the light objects, but not the other way around Slide14: Gilbert’s theory clashed with the older theory proposed by Plutarch Plutarch’s and Gilbert’s theories lived side by side for most of the 17th century. The attraction of electrics was not thought to be of much significance and there were no substantial developments until about 1675Slide15: In 1675 Robert Boyle tested the air theory by using the newly invented vacuum pump. www.humanities.ccny.cuny.edu/history/reader/vacuum.htm Slide16: Boyle found that the electrical attraction exists in vacuum as well, rejected the displaced air theory, and concluded that it must be the direct contact with an effluvium that is the cause of the electric attraction. Boyle’s experiments did not convince the adherents of the air theory. They argued that the vacuum pump does not remove all air, which, incidentally, was a correct assertion. Slide17: In early 1700s, Francis Hauksbee (?-1713) performed experiments during meetings of Royal Society in London. The experiments had to have easily observable effects and Hauksbee chose the phenomenon of barometric light for his demonstrations. Barometric light occurs in the space above the mercury in a barometric tube when the tube is shaken. As the mercury is splashed on the walls of the tube and runs down the glass walls, intermittent flashes of light appear. Slide18: In a barometric tube, the flashes are weak and not always reproducible. Francis Hauksbee used the principle of the barometric tube and built a device that produced a spectacular display of light. Hauksbee guessed that the light display is due to the friction between the glass and the little drops of mercury. From here he progressed to use materials other than mercury and glass, rubbed them together in partial vacuum and observed them to produce flashes of light. Slide19: Hauksbee’s “electric machines”Slide20: A new phenomenon in now growing field of electricity was discovered by Stephen Gray (1667 - 1736). Stephen Gray made a large number of experiments in which he demonstrated that the ability of electrics to attract small objects (he called it the attractive virtue) can be transferred to some materials through a direct contact and carried a significant distance.In his experiments, Gray used hemp thread to conduct the “attractive virtue” as far as 150 m. Could it be that the coincidence of high humidity of British weather aided his experimentations? Slide21: Stephen Gray’s experiments inspired Charles Francois de Cisternay Dufay (1698-1736) in France. Charles Dufay was methodical. He started his investigations by a historical review of the work done before him and proceeded to list the questions he wanted to investigate:Slide22: 1. Can all bodies be made electric by rubbing, and is electricity a common property of matter? 2. Can all bodies receive the electric virtue, either by contact or by close approach of an excited electric? 3. Which bodies stop, and which facilitate the transmission of the virtue; and which bodies are most strongly attracted by an excited electric? 4. What is the relationship between the repulsive and attractive virtues; are they connected or totally independent? 5. Is the strength of electricity augmented or diminished by a void, compressed air, elevated temperature, etc? 6. What is the relation between electricity and the faculty of producing light, which is common to most electric bodies, and what can be inferred from this relation? Slide23: Charles Dufay found that all materials, except metals and soft objects, can be made electric by rubbing. Dufay concluded that electricity is a property of matter. As many experimenters before him, he noticed that rubbed electrics not only attract small objects, but sometimes repel them; however unlike the other investigators he did not dismiss this effect and concluded that there are two kinds of electricities: vitreous, gained by rubbing glass, animal hair, etc., and resinous, gained by rubbing amber, copal, silk and many other materials. Based on the assumption of two types of electricity, Dufay built his theory:: Based on the assumption of two types of electricity, Dufay built his theory: Bodies that are not electrified have an equal amounts of both electricities. If both bodies posses the same type of electricity, they will repel each other; if one body possesses vitreous electricity and the other body possesses resinous electricity, they will attract each other. metals and wet objects conduct electricity; on the other hand materials that make good electrics (amber, glass) do not conduct electricity.Slide25: Around the middle of the 18th century, the interest in electricity spread from England and France to the rest of western Europe. Almost simultaneously, at Kammin in Pomerania, Jurgen von Kleist, and at Leyden in Holland, Pieter Van Musschenbroeck, invented, or, to be more precise, stumbled on, a new device. The device came to be called Leyden jar. Slide26: Leyden jar was a glass container half filled with water into which an electric wire was inserted. The wire was put in contact with an electrical machine. To be effective, the jar had to be held in the palm of the hand by the experimenter. It was capable of storing the electric virtue for several days, and delivering powerful shocks when the same person held the jar and at the same time touched the wire. Pieter Van Musschenbroeck described the moment of his discovery:: Pieter Van Musschenbroeck described the moment of his discovery: “Suddenly I received in my right hand a shock of such violence that my whole body was shaken as by a lightning stroke. The vessel, although of glass, was not fractured, nor was the hand displaced by the commotion; but the arm and body were affected in a manner more terrible than I can well express. In a word, I thought that I was done for.” Slide28: The Leyden jar was later improved by adding conducting layers to the inside and outside of the jar, and eventually it was recognized that it does not need to be in the shape of jar to store electricity, and that it can be filled by the electric fluid from both sides, outside and inside. In this portrait Franklin is 56 years old. Notice the lightning detector to Franklin’s right. : In this portrait Franklin is 56 years old. Notice the lightning detector to Franklin’s right. The experiments with electricity caught attention of Benjamin Franklin in the North American colonies. Slide30: Franklin repeated many experiments that were already well known to English and French electricians - he started his experimenting with rubbing a glass tube. However, his conclusions were very different from the accepted theories. Franklin’s theory: Franklin’s theory When two substances are rubbed together, there is no electricity created by the friction, one substance looses some electricity, and the other receives it; therefore there is only one kind of electricity, not two. One substance therefore is positively electricised, the other negatively. Slide32: Franklin also experimented with the Leyden jar, and again he maintained that the electricity appearing on the conductors inside and outside of the jar is in equal quantities and of opposite signs. One conductor has an excess, the other lack of the electric fluid. Franklin was not well familiar with the vocabulary for the emerging science of electricity. To describe his discoveries, he had to invent some terms. : Franklin was not well familiar with the vocabulary for the emerging science of electricity. To describe his discoveries, he had to invent some terms. Terms he invented are: positive and negative electricity, to charge, meaning to store electricity (in the Leyden jar): To charge a bottle commodiously through the coating, place it on a glass stand; form a communication from the prime conductor to the coating, and another from the hook to the wall or floor. When it is charged, remove the latter communication before you take hold of the bottle, otherwise great part of the fire will escape by it. Slide34: Through his experiments with the Leyden jar, Franklin came to recognize that lightning is electrical in nature. To prove his point, he devised his legendary experiment sending a kite into storm clouds to gather electricity and he succeeded in charging a Leyden jar by conducting the electricity from the cloud through the wet kite string tied to a metal key. Slide35: Not everyone was as lucky as Franklin. Swedish scientist Georg Richman at Saint Petersburg also tried Franklin’s lightning experiment and was instantly killed.Slide36: In spite of the obvious danger of electricity, electrical games and toys became very popular One such game was The Electric Boy. This picture was engraved by William Watson in 1748. Static electricity is generated be turning a crank of a glass or sulfur cylinder that is rubbed by a strip of leather. The charge is transferred to the shoes of a boy suspended on silk ropes. The boy holds his hand above a plate with small pieces of paper or feathers that are attracted to his hand. The girl on the right moves her hand close to boy's nose and receives a shock. Electricity was an element in fashion design: Electricity was an element in fashion designSlide38: In the second half of 18th century some very large electrostatic machines were built. Possibly the largest was built and described by Martinus van Marum in 1785. This electrostatic generator is still on display at Teyler’s Museum in Haarlem, the Netherlands. The two rotating glass discs producing the electricity are more than 5 ft in diameter.Slide39: Franklin’s theory of one electric fluid raised a question of amounts of the electric fluid or electric charge transferred between objects. It was also observed that the attractive or repulsive forces vary in strength. Establishing the relationship between the force and the charges and the distance between the charges became the quest of the scientists following Dufay and Franklin. Slide40: Newton’s work on gravitational force gave rise to an assumption that the electrical force may be described by a similar law. It was expected that the force between two charges will be inversely proportional to the square of their distance and directly proportional to the product of their “electrical masses”. This was confirmed by Charles Augustin Coulomb (1736-1806). www.csvt.qc.ca/patriotes/pei/travaux/coulomb/coulomb.htm Slide41: In early 19th century, the efforts in study of electricity were directed towards finding a steady source of electricity and also towards finding the connection between electricity and magnetism. However, that is another story. OVERVIEW OF THE DEVELOPMENT OF THE THEORIES ABOUT ELECTRICITY : OVERVIEW OF THE DEVELOPMENT OF THE THEORIES ABOUT ELECTRICITY The concept of cause for electrical behaviour of materials underwent many changes over the time. The initial development was rather slow, compared for example to the development of ideas about motion or magnetism, perhaps because the known electric effects of materials were considered quaintly interesting, but without a practical application. Slide43: The initial theories assumed existence of a medium, “an electric effluent”, that would cause movement of objects towards electrified bodies by a direct contact. This notion carried into 18th century, when it underwent first significant changes. The investigators of electric effects concentrated on the effects themselves, describing what they found, simply accepting that this is the way things are, and not speculating on underlaying reasons for their existence. Slide44: Yet they were unable to divorce themselves from the need to imagine some substance responsible for the effects, even though they could not detect any substance. This substance they called electric virtue, and the manifestations of properties of electrified bodies were thought to be due to transfers of electric virtue from one object to another. Slide45: The work of the experimenters of the first half of the 18th century culminated in the theory of two kinds of electricities - vitreous and resinous. It was believed that all bodies have both kinds of electricities in equal amounts and become electrified when part of one type of electricity is removed. In the second half of the 18th century, a rival theory was proposed - saying that there is only one type of electricity (or electric fluid) and the electrified bodies have either surplus or shortage of the electric fluid.Slide46: The 19th century saw the competition between the two theories - the theory of two electric fluids vs the theory of one electric fluid. Each theory had its prominent adherents. Although we now reject the notion of electric fluids, both theories are still reflected in our present theories. Slide47: Our present view is that there are two particles that carry opposite electric charges present in every substance, electrons (negative) and protons (positive). If the substance does not display electric behaviour, both particles are present in equal numbers. In metals or when surface charge is transferred from one object to another, the transfer of charge is due to the excitation of the negative particles. Except for the sign and the quantum character of the particles, this is Franklin’s hypothesis. Slide48: We assume protons to be fixed. However, positive particles, ions, can be created by removal of electrons from atoms or molecules. In gases, the charge can be transferred by either motion of the negative electrons, or of the positive ions, or both, which is close to the Dufay’s two-fluid theory. References: References Bordeau, Sanford P. Volts to Hertz … the rise of electricity Cohen, I. B. Benjamin Franklin’s Science, Harvard University Press, 1990 Cohen, I. B., Album of Science: From Leonardo to Lavoisier, 1450-1800, Charles Scribner’s Sons, 1980 B. Dibner, Alessandro Volta, Franklin Watts Inc., 1964 D. Halliday, R. Resnick, J. Walker, Fundamentals of Physics, 4th edition, John Wiley & Sons, Inc., 1993 J. Priestly, The History and Present State of Electricity, Johnson Reprint Corporation, 1966 Harry Robin, The Scientific Image: From Cave to Computer, Harry N. Abrams, 1992 D. Roller & D. Roller, The Development of the Concept of Electric Charge, Harvard University Press, 1954 A. Still, Soul of Amber, Murray Hill Books Inc., 1944 S. M. Stocklmayer and D. F. Treagust, A Historical Analysis of Electric Currents in Textbooks: A Century of Influence on Physics Education, Second International HPS&ST Proceedings A. Stinner, The Teaching of Physics and the Context of Inquiry: From Aristotle to Einstein, Science Education 73(5), 1989 A. Stinner, The Story of Force: from Aristotle to Einstein, Physics Education, vol. 29, number 2, March 1994 You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.