Electromagnetic Induction and Faradays Law All contents are Copyright © 2016 by AspenCore, Inc. All Rights Reserved. Advertisement Home / Electromagnetism / Electromagnetic Induction Electromagnetic Induction We have seen previously that when a DC current pass through a long straight conductor a magnetising force, H and a static magnetic field, B is developed around the wire. If the wire is then wound into a coil, the magnetic field is greatly intensified producing a static magnetic field around itself forming the shape of a bar magnet giving a distinct North and South pole. Air-core Hollow Coil The magnetic flux developed around the coil being proportional to the amount of current flowing in the coils windings as shown. If additional layers of wire are wound upon the same coil with the same current flowing through them, the static magnetic field strength would be increased. Therefore, the magnetic field strength of a coil is determined by the ampere turns of the coil. With more turns of wire within the coil, the greater the strength of the static magnetic field around it. But what if we reversed this idea by disconnecting the electrical current from the coil and instead of a hollow core we placed a bar magnet inside the core of the coil of wire.

By moving this bar magnet “in” and “out” of the coil a current would be induced into the coil by the physical movement of the magnetic flux inside it. Likewise, if we kept the bar magnet stationary and moved the coil back and forth within the magnetic field an electric current would be induced in the coil. Then by either moving the wire or changing the magnetic field we can induce a voltage and current within the coil and this process is known as Electromagnetic Induction and is the basic principal of operation of transformers, motors and generators. Electromagnetic Induction was first discovered way back in the 1830’s by Michael Faraday. Faraday noticed that when he moved a permanent magnet in and out of a coil or a single loop of wire it induced an ElectroMotive Force or emf, in other words a Voltage, and therefore a current was produced. So what Michael Faraday discovered was a way of producing an electrical current in a circuit by using only the force of a magnetic field and not batteries. This then lead to a very important law linking electricity with magnetism, Faraday’s Law of Electromagnetic Induction. So how does this work?.

When the magnet shown below is moved “towards” the coil, the pointer or needle of the Galvanometer, which is basically a very sensitive centre zero’ed moving-coil ammeter, will deflect away from its centre position in one direction only. When the magnet stops moving and is held stationary with regards to the coil the needle of the galvanometer returns back to zero as there is no physical movement of the magnetic field. Likewise, when the magnet is moved “away” from the coil in the other direction, the needle of the galvanometer deflects in the opposite direction with regards to the first indicating a change in polarity. Then by moving the magnet back and forth towards the coil the needle of the galvanometer will deflect left or right, positive or negative, relative to the directional motion of the magnet. Electromagnetic Induction by a Moving Magnet Likewise, if the magnet is now held stationary and ONLY the coil is moved towards or away from the magnet the needle of the galvanometer will also deflect in either direction. Then the action of moving a coil or loop of wire through a magnetic field induces a voltage in the coil with the magnitude of this induced voltage being proportional to the speed or velocity of the movement.

Then we can see that the faster the movement of the magnetic field the greater will be the induced emf or voltage in the coil, so for Faraday’s law to hold true there must be “relative motion” or movement between the coil and the magnetic field and either the magnetic field, the coil or both can move. Faraday’s Law of Induction From the above description we can say that a relationship exists between an electrical voltage and a changing magnetic field to which Michael Faraday’s famous law of electromagnetic induction states: “that a voltage is induced in a circuit whenever relative motion exists between a conductor and a magnetic field and that the magnitude of this voltage is proportional to the rate of change of the flux”. In other words, Electromagnetic Induction is the process of using magnetic fields to produce voltage, and in a closed circuit, a current. So how much voltage (emf) can be induced into the coil using just magnetism. Well this is determined by the following 3 different factors. 1).

Increasing the number of turns of wire in the coil – By increasing the amount of individual conductors cutting through the magnetic field, the amount of induced emf produced will be the sum of all the individual loops of the coil, so if there are 20 turns in the coil there will be 20 times more induced emf than in one piece of wire. 2). Increasing the speed of the relative motion between the coil and the magnet – If the same coil of wire passed through the same magnetic field but its speed or velocity is increased, the wire will cut the lines of flux at a faster rate so more induced emf would be produced. 3). Increasing the strength of the magnetic field – If the same coil of wire is moved at the same speed through a stronger magnetic field, there will be more emf produced because there are more lines of force to cut. If we were able to move the magnet in the diagram above in and out of the coil at a constant speed and distance without stopping we would generate a continuously induced voltage that would alternate between one positive polarity and a negative polarity producing an alternating or AC output voltage and this is the basic principal of how a Generator works similar to those used in dynamos and car alternators.

In small generators such as a bicycle dynamo, a small permanent magnet is rotated by the action of the bicycle wheel inside a fixed coil. Alternatively, an electromagnet powered by a fixed DC voltage can be made to rotate inside a fixed coil, such as in large power generators producing in both cases an alternating current. Simple Generator using Magnetic Induction The simple dynamo type generator above consists of a permanent magnet which rotates around a central shaft with a coil of wire placed next to this rotating magnetic field. As the magnet spins, the magnetic field around the top and bottom of the coil constantly changes between a north and a south pole. This rotational movement of the magnetic field results in an alternating emf being induced into the coil as defined by Faraday’s law of electromagnetic induction.

The magnitude of the electromagnetic induction is directly proportional to the flux density, β the number of loops giving a total length of the conductor, l in meters and the rate or velocity, ν at which the magnetic field changes within the conductor in meters/second or m/s, giving by the motional emf expression: Faraday’s Motional emf Expression If the conductor does not move at right angles (90°) to the magnetic field then the angle θ° will be added to the above expression giving a reduced output as the angle increases: Lenz’s Law of Electromagnetic Induction Faraday’s Law tells us that inducing a voltage into a conductor can be done by either passing it through a magnetic field, or by moving the magnetic field past the conductor and that if this conductor is part of a closed circuit, an electric current will flow. This voltage is called an induced emf as it has been induced into the conductor by a changing magnetic field due to electromagnetic induction with the negative sign in Faraday’s law telling us the direction of the induced current (or polarity of the induced emf). But a changing magnetic flux produces a varying current through the coil which itself will produce its own magnetic field as we saw in the Electromagnets tutorial.

This self-induced emf opposes the change that is causing it and the faster the rate of change of current the greater is the opposing emf. This self-induced emf will, by Lenz’s law oppose the change in current in the coil and because of its direction this self-induced emf is generally called a back-emf. Lenz’s Law states that: ” the direction of an induced emf is such that it will always opposes the change that is causing it”. In other words, an induced current will always OPPOSE the motion or change which started the induced current in the first place and this idea is found in the analysis of Inductance . Likewise, if the magnetic flux is decreased then the induced emf will oppose this decrease by generating and induced magnetic flux that adds to the original flux. Lenz’s law is one of the basic laws in electromagnetic induction for determining the direction of flow of induced currents and is related to the law of conservation of energy. According to the law of conservation of energy which states that the total amount of energy in the universe will always remain constant as energy can not be created nor destroyed. Lenz’s law is derived from Michael Faraday’s law of induction. One final comment about Lenz’s Law regarding electromagnetic induction.

We now know that when a relative motion exists between a conductor and a magnetic field, an emf is induced within the conductor. But the conductor may not actually be part of the coils electrical circuit, but may be the coils iron core or some other metallic part of the system, for example, a transformer. The induced emf within this metallic part of the system causes a circulating current to flow around it and this type of core current is known as an Eddy Current. Eddy currents generated by electromagnetic induction circulate around the coils core or any connecting metallic components inside the magnetic field because for the magnetic flux they are acting like a single loop of wire. Eddy currents do not contribute anything towards the usefulness of the system but instead they oppose the flow of the induced current by acting like a negative force generating resistive heating and power loss within the core. However, there are electromagnetic induction furnace applications in which only eddy currents are used to heat and melt ferromagnetic metals. Eddy Currents Circulating in a Transformer The changing magnetic flux in the iron core of a transformer above will induce an emf, not only in the primary and secondary windings, but also in the iron core.

The iron core is a good conductor, so the currents induced in a solid iron core will be large. Furthermore, the eddy currents flow in a direction which, by Lenz’s law, acts to weaken the flux created by the primary coil. Consequently, the current in the primary coil required to produce a given B field is increased, so the hysteresis curves are fatter along the H axis. Laminating the Iron Core Eddy current and hysteresis losses can not be eliminated completely, but they can be greatly reduced. Instead of having a solid iron core as the magnetic core material of the transformer or coil, the magnetic path is “laminated”. These laminations are very thin strips of insulated (usually with varnish) metal joined together to produce a solid core. The laminations increase the resistance of the iron-core thereby increasing the overall resistance to the flow of the eddy currents, so the induced eddy current power-loss in the core is reduced, and it is for this reason why the magnetic iron circuit of transformers and electrical machines are all laminated. Energy and kids Faraday's inventions Magnetism Faraday's greatest work was with electricity.

In 1821, soon after the Danish chemist, Hans Christian Orsted, discovered the phenomenon of magnetism, Humphry Davy and William Hyde Wollaston tried but failed to design an electric motor. Faraday, having discussed the problem with the two men, went on to build two devices to produce what he called electromagnetic rotation which is a continuous circular motion from the circular magnetic force around a wire. A wire extending into a pool of mercury with a magnet placed inside would rotate around the magnet if charged with electricity by a chemical battery. This device is known as a homopolar motor. These experiments and inventions form the foundation of modern electromagnetic technology. Unwisely, Faraday published his results without acknowledging his debt to Wollaston and Davy, and the resulting controversy caused Faraday to withdraw from electromagnetic research for several years. * * * Faraday's first dynamo Ten years later, in 1831, he began his great series of experiments in which he discovered electromagnetic induction. He found that if he moved a magnet through a loop of wire, an electric current flowed in the wire. The current also flowed if the loop was moved over a stationary magnet.

This was the first transformer (inductor), although Faraday used it only to demonstrate the principle of electromagnetic induction and did not realise what it would eventualybe used for. His experiments established that a changing magnetic field produces an electric field. This relation was mathematically modelled by faraday's law, which afterwards became one of the four Maxwell equations. These in turn evolved into the generalization known as field theory. Faraday then used this principle to construct the first dynamo (in the form of a copper disk rotated between the poles of a permanent magnet), the predecessor of modern dynamos and generators. * * * Faradayï¿½s first electric generator In 1831-1832 Michael Faraday discovered that a potential difference is generated between the ends of an electrical conductor that moves perpendicular to a magnetic field. He also built the first electromagnetic generator called the 'Faraday disc', a type of homopolar generator, using a copper disc rotating between the poles of a horseshoe magnet. It produced a small DC voltage, and large amounts of current. This design was inefficient due to self-cancelling counterflows of current in regions not under the influence of the magnetic field.

While current flow was induced directly underneath the magnet, the current would circulate backwards in regions outside the influence of the magnetic field. This counterflow limits the power output to the pickup wires, and induces waste heating of the copper disc. Later homopolar generators would solve this problem by using an array of magnets arranged around the disc perimeter to maintain a steady field effect in one current-flow direction. * * * Farady's disk This exemplar of Faraday's disk is currently in the Marischal museum in Aberdeen. It is approximately 75 centimeters long and 26 centimeters wide and measures 19 centimeter in the diameter. This apparatus can be considered to be the first dynamo ever made, capable of producing electricity by making a copper disk spin between two magnets. It was made and used in several experiments by Michael Faraday around the 1850's. On this particular model, there is actually no magnet; the copper disk is so thin that the earths own magnetic field is sufficient to make the apparatus work. There was also some mercury on the contacts on the disk, but it is now absent. Michael Faraday had constructed Faraday's disk to demonstrate and visualise the theory about currents and magnetic fields he had discovered.

Unfortunately, the disk was very inefficient in producing current and was never actually used as a practical power source, but only as a tool of demonstration. Other scientists, with Nikola Tesla amongst them as one of the earliest to take profit of Faraday's invention, later improved and changed Faraday's disk. Tesla patented a version of Faraday's disk which had less frictional losses and Hippolyte Pixii constructed the first efficient dynamo by adding a commutator to it. Sir Mark Oliphant was inspired by it to build what became the world's largest homopolar generator (producing 500 Megajoules). Faraday's disk helped a wide range of scientists, such as Sir Joseph Larmour, to understand more phenomena. In Larmour's case, the newly found link between magnetic fields and current lead him to an explanation of several phenomena related to sunspots. Zï¿½nobe Gramme used the principle of Faraday's disk to design the first commercial power plants in Paris, discovering what is since then known as the basic concept of a spinning endless loop of wires. Later, Joseph Newmann invented the axletree dynamo, which was believed to be a perpetual motion dynamo but was never patented.

* * * Faraday law of electrolysis In 1832, Michael Faraday reported that the quantity of elements separated by passing an electrical current through a molten or dissolved salt was proportional to the quantity of current passed through the circuit. This became the basis of the first law of electrolysis. He also popularized terminology such as anode, cathode, electrode, and ion. * * * Faraday effect In 1845 he discovered what is now called the Faraday effeact. The plane of polarization of linearly polarized light propagated through a material medium can be rotated by the application of an external magnetic field aligned in the propagation direction. He wrote in his notebook, "I have at last succeeded in illuminating a magnetic curve or line of force and in magnetising a ray of light". This established that magnetic force and light were related. * * * Diamagnetism In 1845 he also discovered the phenomenon that he named Diamagnetism - a very weak form of magnetism that is only exhibited in the presence of an external magnetic field. This phenomenon can can be used for levitation.

* * * Faraday cage In his work on static electricity, Faraday demonstrated that the charge only resided on the exterior of a charged conductor, and exterior charge had no influence on anything enclosed within a conductor. This is because the exterior charges redistribute such that the interior fields due to them cancel. This shielding effect is used in what is now known as a Faraday cage. The Faraday cage is a practical application of the effect demonstrated in school as the Faraday ice-pail experiment. If an ice pail, or any other hollow conductor is given a charge on its inside, then the charge will spread all over the outside surface of the conductor in such a way as to produce no electric field inside. The Van de Graaff generator uses this effect to produce such a large potential on the outside surface of its dome. In large Van de Graaff generators it is possible to have a lab or office actually inside the dome, and even have people there, while the machine is on! The idea that a hollow metal conductor will protect the interior from electric fields can be used using Faraday screens, cans or cages. A Faraday can is nothing more complicated that a metal biscuit barrel for example.

If an electronic watch is placed inside such a container, and then a spark is drawn to the container either from a Van de Graaff generator or induction coil, then after the demonstration, the watch will be unharmed. A more impressive demonstration of the Faraday cage effect is that of an aircraft being struck by lightning. This happens frequently, but does not harm the plane or passengers. The metal body of the aircraft protects the interior. For the same reason, and if it were not for the highly flammable nature of petrol, a car would be a very safe place to be in a thunderstorm. Demonstration of the Faraday cage effect: A human-size Faraday cage has been constructed. Lets allow someone to stand inside while the discharge from a Tesla coil is directed towards it. To increase the dramatic content of the demonstration, the person inside is asked to hold a fluorescent tube, which does not light, while similar tubes balanced against the sides of the cage do light when the discharge is enabled. Our cage measures 1m square and is 2m tall. It is built from 1cm pitch steel mesh.

The mesh is secured to a strong 'speedframe' framework, and riveted all round the frame except for the door section which is hinged on, and has two retainer catches to ensure the door stays shut while the demonstration is taking place. When the cage is charged, the pith balls move away from the outside of the cage, indicating the presence of an electric field, but the pith balls inside the cage are not repelled, indicating that there is no electric field inside the conductor. * * * Benzene Faraday also dabbled in chemistry, discovering chemical substances such as benzene, inventing the system of oxidization numbers, and liquefying gases. Faraday and the Electromagnetic Theory of Light - OpenMind Faraday and the Electromagnetic Theory of Light Faraday and the Electromagnetic Theory of Light Share Sign in or register to rate this publication Michael Faraday (1791-1867) is probably best known for his discovery of electromagnetic induction, his contributions to electrical engineering and electrochemistry or due to the fact that he was responsible for introducing the concept of field in physics to describe electromagnetic interaction. But perhaps it is not so well known that he also made fundamental contributions to the electromagnetic theory of light.

In 1845, just 170 years ago, Faraday discovered that a magnetic field influenced polarized light – a phenomenon known as the magneto-optical effect or Faraday effect. To be precise, he found that the plane of vibration of a beam of linearly polarized light incident on a piece of glass rotated when a magnetic field was applied in the direction of propagation of the beam. This was one of the first indications that electromagnetism and light were related. The following year, in May 1846, Faraday published the article Thoughts on Ray Vibrations , a prophetic publication in which he speculated that light could be a vibration of the electric and magnetic lines of force. Michael Faraday (1791-1867) / Credits: Wikipedia Faraday’s case is not common in the history of physics: although his training was very basic, the laws of electricity and magnetism are due much more to Faraday’s experimental discoveries than to any other scientist. He discovered electromagnetic induction, which led to the invention of the dynamo, the forerunner to the electric generator.

He explained electrolysis in terms of electrical forces and also introduced concepts such as field and lines of force, which not only were fundamental to understanding electrical and magnetic interactions but also formed the basis of further advances in physics. Michael Faraday was born in South London to a humble family. The only basic formal education he received was in reading, writing and arithmetic as a child. He left school when he was thirteen and started working in a bookbinding shop. His passion for science was awakened by the description of electricity he read in a copy of the Encyclopædia Britannica he was binding, after which he started experimenting in an improvised laboratory. Faraday was hired in 1813 as Humphry Davy’s laboratory assistant at the Royal Institution in London, where he was elected a member in 1824 and where he worked until his death in 1867, first as Davy’s assistant, then as his collaborator, and finally, after Davy’s death, as his succesor. Faraday made such an impression on Davy that when the latter was asked about his greatest discovery, Davy answered: “My greatest discovery was Michael Faraday”.

In 1833 he became the first Fullerian Professor of Chemistry at the Royal Institution. Faraday is also recognized as a great popularizer of science. In 1826 Faraday established the Friday Evening Discourses at the Royal Institution, which are a channel of communication between scientists and laymen. The following year he launched the Christmas Lectures for young people -now broadcast on national television every year-, a series whose objective is to present science to the general public. Faraday himself gave many of these lectures. Both of them continue to this day. Michael Faraday delivering a Christmas Lecture at the Royal Institution in 1856 / Credits: Wikipedia Faraday made his first discovery of electromagnetism in 1821. He repeated Oersted’s experiment placing a small magnet around a current-carrying wire and verified that the force exerted by the current on the magnet was circular. As he explained years later, the wire was surrounded by an infinite series of circular concentric lines of force, which he termed the magnetic field of the current.

He took the work of Oersted and Ampère on the magnetic properties of electrical currents as a starting point and in 1831 achieved an electrical current from a changing magnetic field, a phenomenon known as electromagnetic induction. He found that when an electrical current was passed through a coil, another very short current was generated in a nearby coil. This discovery marked a decisive milestone in the progress not only of science but also of society, and is used today to generate electricity on a large scale in power stations. This phenomenon reveals something new about electric and magnetic fields. Unlike electrostatic fields generated by electric charges at rest whose circulation along a closed path is zero (a conservative field), the circulation of electric fields created by magnetic fields is along a closed path other than zero. This circulation, which corresponds to the induced electromotive force, is equal to the rate of change of the magnetic flux passing through a surface whose boundary is a wire loop ( Faraday’s law of induction ). Faraday invented the first electric motor, the first electrical transformer, the first electric generator and the first dynamo, so Faraday can be called, without any doubt, the father of electrical engineering.

Faraday abandoned the fluid theory to explain electricity and magnetism and introduced the concepts of field and field lines, moving away from the mechanistic explanation of natural phenomena like Newton’s actions-at-a-distance. Faraday’s introduction of the concept of field into physics is perhaps his most important contribution and was described by Einstein as the great change in physics because it provided electricity, magnetism and optics with a common framework of physical theories. However, Faraday’s lines of force were not accepted until several years later when James Clerk Maxwell entered the picture. As noted at the beginning of this article, another and perhaps less known effect discovered by Faraday was the influence of a magnetic field on polarized light, a phenomenon known as the Faraday effect or magneto-optical effect. Faraday’s inquisitive mind was not content to simply discover the relationship between electricity and magnetism. He also wanted to determine whether magnetic fields had an effect on optical phenomena. He believed in the unity of all the forces of nature, and in particular of light, electricity and magnetism.

On September 13, 1845 he found that the plane of polarization of linearly polarized light is rotated when this light travels through a material to which a strong magnetic field is applied in the direction of propagation of the light. Faraday wrote in paragraph #7504 of his Dairy: “Today worked with lines of magnetic force, passing them across different bodies (transparent in different directions) and at the same time passing a polarized ray of light through them (…) there was an effect produced on the polarized ray, and thus magnetic force and light were proved to have relation to each other”. This was certainly the first clear indication that magnetic force and light were related to each other and it also showed that light is related to electricity and magnetism. In relation to this phenomenon Faraday also wrote in the same paragraph: “This fact will most likely prove exceedingly fertile and of great value in the investigation of both conditions of natural force”. He was not wrong. This effect is one of the cornerstones of the electromagnetic theory of light.

Polarization rotation due to the Effect Faraday / Credits: Adapted from Wikipedia In a Royal Institution’s Friday Evening Discourse delivered on April 1846, Faraday speculated that light might be some form of disturbance propagating along the field lines. The truth is that on this particular Friday it was Charles Wheatstone who was scheduled to give a talk on his chronoscope. However, at the last minute, Wheatstone had an attack of stage fright and so Faraday delivered Wheatstone’s talk. Since he finished ahead of time, he filled in the remaining minutes by revealing his thoughts on the nature of light. Faraday’s discourse was published the same year in the Philosophical Magazine under the title Thoughts on Ray-Vibrations . Faraday even dared to question the existence of the luminiferous aether –a scientific heresy at that time–, which was supposed to be the medium for light propagation as so elegantly Fresnel had described in his wave theory of light. He proposed that the light could be not the result of aether vibrations, but vibrations of the physical lines of force. Faraday tried to leave out the aether, but he kept the vibrations.

In an almost apologetic tone, Faraday finishes his paper stating: “I think it likely that I have made many mistakes in the preceding pages, for even to myself, my ideas on this point appear only as the shadow of a speculation”. However, this idea of Faraday’s was received with considerable scepticism and rejected by everyone until Maxwell’s article titled A Dynamical Theory of the Electromagnetic Field was published in 1865. In this paper, Maxwell not only describes his seminal electromagnetic theory of light –one of the milestones commemorated in this International Year of Light 2015 – but also attributes the ideas which eventually formed the basis of his theory to Faraday’s thoughts on ray vibrations. On page 466 of his paper, and with the modesty that always characterized Maxwell, he refers to Faraday’s 1846 paper as follows: “The conception of the propagation of transverse magnetic disturbances to the exclusion of normal ones is distinctly set forth by Professor Faraday in his ‘Thoughts on Ray Vibrations’.

The electromagnetic theory of light, as proposed by him [Faraday], is the same in substance as that which I have begun to develop in this paper, except that in 1846 there were no data to calculate the velocity of propagation”. And on page 461 of his 1865 paper Maxwell also refers to the magneto-optical effect, stating: “Faraday discovered that when a plane polarized ray transverses a transparent diamagnetic medium in the direction of the lines of magnetic force produced by magnets or currents in the neighbourhood, the plane of polarization is caused to rotate”. In all Michael Faraday is cited six times and mentioned three times in Maxwell’s 1865 paper. However, this is not surprising considering that a large amount of Maxwell’s work is based on Faraday’s work and Maxwell mathematically modelled most of Faraday’s discoveries on electromagnetism into the theory that we know today. The electromagnetic waves about whose existence Faraday speculated in 1846 with his thoughts on ray vibrations, and which were mathematically predicted by Maxwell in 1865, were finally produced in a laboratory by Hertz in 1888. The rest is history.

It is clear that Maxwell opened the door to twentieth century physics, but it is no less clear that Faraday gave Maxwell some of the keys he used. In 1676 Newton sent a letter to his rival Hooke in which he wrote: “If I have seen further, it is by standing on the shoulders of Giants” (*). Two hundred and fifty years later, during one of Einstein’s visits to Cambridge, UK, someone remarked: “You have done great things, but you stand on Newton’s shoulders”. Einstein replied: “No, I stand on Maxwell’s shoulders”. If someone had said the same to Maxwell, he would probably have said that he stood on Faraday’s shoulders. (*) Although this sentence is interpreted by some authors as a sarcastic remark directed at Hooke’s hunchback appearance, nowadays the phrase is usually used in a positive way. Now Newton’s comment is a claim how science is a series of incremental advances reach of which is built on those previously reached (see, for example, Stephen Hawking’s book titled On the Shoulders of Giants).

Bibliography The Dynamo Process For some unusual examples of this dynamo process, see the web sites about the dynamo involving Jupiter's moon Io and about the space tether experiment on the Space Shuttle . Faraday's disk dynamo needs a magnetic field in order to produce an electric current. Is it possible for the current which it generated to also produce the magnetic field which the dynamo process required? That, in a nutshell, was what Larmor proposed was happening in sunspots. At first sight this looks like a "chicken and egg" propostion: to produce a chicken, you need an egg, but to produce an egg you need a chicken--so which of these came first? Similarly here--to produce a current, you need a magnetic field, but to produce a magnetic field you need a current. Where does one begin? Actually, weak magnetic fields are always present and would be gradually amplified by the process, so this poses no obstacle. One could, for instance, link two Faraday dynamos, each supplying the current needed to produce the other's magnetic field. They could (in principle) form a feasible self-excited dynamo, deriving its energy from whatever force was turning the disks.

However, whether a fluid dynamo could mimic this behavior--e.g. swirls of fluid flow in a tank of liquid mercury--is a much harder question and took decades to resolve. (More about dynamos in the next section and in part #14 of * now read it backwards Exploring Further The book "Michael Faraday and the Nature of Electricity" by Roberta Baxter (144 pp, Morgan Reynolds publishing, Greensboro, North Carolina, 2009) tells of Faraday's life and work. A slim book probably meant for teen-agers, it is nevertheless rather detailed and quite readable. Optional (Mainly for Teachers) When the shaft of a dynamo is turned by some outside force, its electrical connections can produce an electric current. Many dynamos however are reversible: if an electric current is fed into its electrical connection, the force on the current can turn the same shaft, converting the dynamo into a motor. In some models of "hybrid" automobiles, electric motors fed by a storage battery help the gasoline engine accelerate the car, but then when the car slows down, they become dynamos and feed an electric current back into the battery, saving energy which otherwise might turn into waste heat in brakes.

The Faraday disk dynamo can also reverse and become a motor, though a rather inefficient one. A tabletop demonstration of this is described in "Magnetic Force on an Electrolyte" by Marián Kireš and Zuzana Ješkova, on p. 50-51 of "The Physics Teacher," Vol. 45, January 2007. The rotating disk here is a shallow layer of water containing copper sulfate, which conducts electricity. The solution in put in a Petri dish and placed on top of one of the poles of a vertical laboratory electromagnet; little pieces of cork floating on the fluid then trace its rotation The electrodes are two circles of copper (they can be sawed from the ends of pipes)--a big one on the outer boundary of the solution and a small one in the middle. When the terminals of a battery of an electric power supply are connected to the two copper circles, the fluid starts rotating. Reverse the contacts and the rotation reverses too.

Inventor Michael Faraday Michael Faraday Father of Electronics by Charles Ludwig / Paperback (May 1988) / Herald Pr Ludwig retells Michael Faraday's remarkable life story in fictionalized form, presenting the man who invented the electric motor, the dynamo, the transformer, and the generator. by Michael Faraday, Peter Day (Compiler) / Paperback - 212 pages / Inst of Physics Pub (1999) An attractive collection that serves well as an introduction to this extraordinary man. Michael Faraday by Geoffrey Cantor, David Gooding / Paperback (October 1996) / Humanity Books This biography follows his early life and career, his role in the Royal Institution and in civic and military science, and his influence on science and engineering. by Michael Faraday / Paperback - 88 pages (May 1993) / Prometheus Books Certainly a true classic. This book will appeal to both the layman and the technically inclined. by James Clerk Maxwell / Paperback 3rd edition (January 1991) / Dover Pubns This volume covers magnetism and electromagnetism.

ON THE WEB: A complete edition of Faraday's approximately 4800 extant letters is being published under the editorship of Frank James at the Royal Institution. Brief overviews of each volume are given. (URL: His discoveries have had an incalculable effect on subsequent scientific and technical development. He was a true pioneer of scientific discovery. Presented by the Institution of Electrical Engineers. (URL: Earth begins to emit a noticeable glow! During the early 19th century, newspaper headlines across Europe cried out " Napoleon escapes from St. Elba... Continental armies on the march!! During the same period, these newspapers barely noted Michael Faraday's discovery of the kinetic flashlight. Fifty years later, Napoleon was gone, however due to Faraday's discovery, for the first time in it's five billion year history, the night side of the earth began to emit a noticeable glow! (URL: ANOTHER OPINION "I discovered the principle of electromagnetic induction, not Michael Faraday." Joseph Henry (1797-1878) is widely considered the foremost American scientist of the 19th century.

Although Henry at an early age appeared to be headed for a career in the theater, a chance encounter with a book of lectures on scientific topics turned his interest to science. Henrys early investigations concerned electromagnetic phenomena, and his discovery of electromagnetic self-induction in 1831 established his reputation in America. Interestingly, Henry appears to have discovered the principle of electromagnetic induction independently of British scientist Michael Faraday, but because Faraday published his results before Henry, he is credited with the discovery. In 1846 Henry was named first Secretary of the newly-established Smithsonian Institution, a position he held until his death. In 1868 he was elected President of the Academy; this position, too, he held until his death. This according to the National Academy of Sciences, an advisor board to the government in scientific matters. (URL: Electronic Text version of "Faraday as A Discoverer (Page removed from site.) By JOHN TYNDALL From the Fifth Edition, published Longmans, Green, and Co.

London 1894 ( Gutenberg E-text Project) (URL: ftp://uiarchive.cso.uiuc.edu/pub/etext/gutenberg/etext98/fdayd10.txt) DID YOU KNOW?: To honor his accomplishments, a unit of electricity was named after Michael Faraday. The "farad" measures capacitance, an amount of electrical charge. Reference Sources in BOLD Type This page revised Generators and Dynamos Development and History of the component that made electricity first commercially feasible Dynamos and Generators convert mechanical rotation into electric power. Dynamo - a device that makes direct current electric power using electromagnetism. It is also known as a generator, however the term generator normally refers to an "alternator" which creates alternating current power . Generator - normally this term is used to describe an alternator which creates AC power using electromagnetism. Generators, Dynamos, and Batteries are the three tools necessary to create/store substantial amounts of electricity for human use. Batteries may have been discovered as early as 248 BC. They simply use chemical reaction to make and store electricity. Scientists experimented with the battery to invent the early incandescent lamp, electric motors and trains, and scientific tests.

However batteries were not reliable or cost effective for any regular electrical use, it was the dynamo that radically changed electricity from a curiosity into a profitable, reliable technology. 1.) How it Works: Basic: First you need a mechanical power source like a turbine(powered by water falling), wind turbine, gas turbine or steam turbine. A shaft from one of these devices is connected to a generator to make power. Dynamos and generators work using the wild complex phenomena of electromagnetism. Understanding the behavior of electromagnetism, its fields and its effects is a large subject of study. There is a reason why it took 60 years AFTER Volta's first battery to get a good powerful dynamo working. We will keep things simple to help introduce you to the interesting subject of power generation. In the most basic sense a generator/dynamo is one magnet rotating while inside the influence of another magnet's magnetic field. You cannot see a magnetic field, but it is often illustrated using lines of flux. In the illustration above lines of magnetic flux would follow the lines created by the iron filings.

The generator/dynamo is made up of stationary magnets (stator) which create a powerful magnetic field, and a rotating magnet (rotor) which distorts and cuts through the magnetic lines of flux of the stator. When the rotor cuts through lines of magnetic flux it makes electricity. But why? Due to Faraday's Law of Induction if you take a wire and move it back and forth in a magnetic field, the field pushes on electrons in the metal. Copper has 27 electrons, the last two in the orbit are easily pushed on to the next atom. This movement of electrons is electrical flow. See the video below showing how current is induced in a wire: If you take a lot of wire such as in a coil and move it in the field, you create a more powerful "flow" of electrons. The strength of your generator depends on: "l"-Length of the conductor in the magnetic field "v"-Velocity of the conductor (speed of the rotor) "B"-Strength of the electromagnetic field You can do calculations using this formula: e = B x l x v See the video to see all of this demonstrated: About the magnets: Above: a simple electromagnet referred to as a solenoid.

The term "solenoid" actually describes the tubular shape created by the coiled wire. The magnets are usually not made of natural magnetite or a permanent magnet (unless it is a small generator), but they are copper or aluminum wire coiled around an iron core. Each coil must be energized with some power to make it into a magnet. This coil around iron is called a solenoid. Solenoids are used instead of natural magnetite because the solenoid is MUCH more powerful. A small solenoid can create a very strong magnetic field. Above: The coils of wire in the generators must be insulated. Generator failure is caused by temperatures rising too high which results in a breakdown of insulation and a short between to parallel wires. Learn more about wires > Terms: Also see our page on Induction . The Dynamo Dynamo is an older term used to describe a generator that makes direct current power. DC power sends electrons in only one direction. The problem with a simple generator is that when the rotor rotates it eventually turns completely around, reversing the current. Early inventors didn't know what to do with this alternating current, alternating current is more complex to control and design motors and lights for.

Early inventors had to figure a way to only capture the positive energy of the generator, so they invented a commutator. The commutator is a switch that allows current to only flow in one direction. See the video below to see how the commutator works: The Dynamo consists of 3 major components: the stator, the armature, and the commutator. Brushes are part of the commutator, the brushes must conduct electricity as the keep contact with the rotating armature. The first brushes were actual wire "brushes" made of small wires. These wore out easily and they developed graphic blocks to do the same job. The stator is a fixed structure that makes magnetic field, you can do this in a small dynamo using a permanent magnet. Large dynamos require an electromagnet. The armature is made of coiled copper windings which rotate inside the magnetic field made by the stator. When the windings move, they cut through the lines of magnetic field. This creates pulses of electric power. The commutator is needed to produce direct current.

In direct current power flows in only one direction through a wire, the problem is that the rotating armature in a dynamo reverses current each half turn, so the commutator is a rotary switch that disconnects the power during the reversed current part of the cycle. Self excitation: Since the magnets in an dynamo are solenoids, they must be powered to work. So in addition to brushes which tap power to go out to the main circuit, there is another set of brushes to take power from from the armature to power the stator's magnets. That's fine if the dynamo is running, but how do you start a dynamo if you have no power to start? Sometimes the armature retains some magnetism in the iron core, and and when it begins to turn it makes a small amount of power, enough to excite the solenoids in the stator. Voltage then begins to rise until the dynamo is at full power. If there is no magnetism left in the armature's iron, than often a battery is used to excite the solenoids in the dynamo to get it started. This is called "field flashing".

Below in the discussion of wiring the dynamo you will notice how power is routed through the solenoids differently. There are two ways of wiring a dynamo: series wound and shunt wound . See the diagrams to learn the difference. Below, video of a small simple dynamo similar to the diagrams above (built in the 1890s): The Generator The generator differs from the dynamo in that it produces AC power. Electrons flow in in both directions in AC power. It wasn't until the 1890s that engineers had figured out how to design powerful motors, transformers and other devices which could use AC power in a way that could compete with DC power. While the alternator uses commutators, the generator uses a slip ring with brushes to tap the power off of the rotor. Attached to the slip ring are graphite or carbon "brushes" which are spring loaded to push the brush onto the ring. This keeps power consistently flowing. Brushes get worn down over time and need to be replaced.

Below, video of slip rings and brushes, many examples from old to new: Since the time of Gramme in the 1860s it was figured out that the best way to build a dynamo/generator was to arrange magnetic coils around a wide circle, with a wide spinning armature. This looks different than the simple small dynamo examples you see used in teaching how the devices work. In the photo below you will see clearly one coil on the armature (the rest were removed for servicing) and other coils built into the stator. From the 1890s until today 3 phase AC power has been the standard form of power. Three phases is made through the design of the generator. To make a three phase generator you have to place a certain number of magnets on your stator and armature, all with proper spacing. Electromagnetism is as complex as dealing with waves and water, so you need to know how to control the field through your design. Problems include having your magnet unevenly attracted to the iron core, improper calculations of the distortion of the magnetic field (the faster it spins, the more the field is distorted), spurious resistance in the armature coils, and a myriad of other potential problems.

Why 3 phase? if you want to know more about phases and why we use 3 phase, see our video with power transmission pioneer Lionel Barthold. 2.) A Brief History of Dynamos and Generators: The generator evolved from work by Michael Faraday and Joseph Henry in the 1820s. Once these two inventors discovered and documented the phenomena of electromagnetic induction, it lead to experimentation by others in both Europe and North America. 1832 - Hippolyte Pixii (France) built the first dynamo using a commutator, his model created pulses of electricity separated by no current. He also by accident created the first alternator. He did not know what to do with the changing current, he concentrated on trying to eliminate the alternating current to get DC power, this led him to create the commutator. 1830s-1860s - The battery is still the most powerful way to supply electricity for the various experimentation going on in that period. Electricity was still not commercially viable. A battery powered electric train from Washington DC to Baltimore failed, proving a gross embarrassment to the new field of electricity. After millions of dollars wasted steam still proved to be a better power source.

Electricity still needed to prove to be reliable and commercially viable. 1860 - Antonio Pacinotti- Created a dynamo that provided continuous DC power 1867 - Werner Von Siemens and Charles Wheatstone create a more powerful, more useful dynamo which used a self powered electromagnet in the stator instead of the weak permanent magnet. 1871 - Zenobe Gramme sparked the commercial revolution of electricity. He filled the magnetic field with an iron core which made a better path for magnetic flux. This increased the power of the dynamo to the point were it was usable for many commercial applications. 1870s - There was an explosion of new designs in dynamos, designs ranged a wild assortment, only a few stood out as being superior in efficiency. 1876 - Charles F. Brush (Ohio) developed the most efficient and reliable dynamo design ever to that point. His inventions was sold through the Telegraph Supply Company. 1877 - The Franklin Institute (Philadelphia) conducts test on dynamos from around the world. Publicity from this event spurs development by others like Elihu Thomson , Lord Kelvin, and Thomas Edison .

Above: Edison's Long Legged Mary, a commercially successful dynamo for his DC systems 1884 1878 - The Ganz Company begins to use AC generators in small commercial installations in Budapest. 1880 - Charles F. Brush had over 5000 arc lights in operation, representing 80 percent of all lamps world wide. The economic power of electrical age had begun. 1880-1886 - Alternating Current systems develop in Europe with Siemens, Sabastian Ferranti, Lucien Gaulard, and others. DC dynamos reign supreme in the lucrative American market, many are skeptical to invest in AC. AC generators were powerful, however the generator alone was not the biggest problem. Systems for control and distribution of AC power needed to be improved before it could compete with DC on a market. 1886 - In the North American Market inventors like William Stanley , George Westinghouse, Nikola Tesla, and Elihu Thomson develop their own AC systems and generator designs. Most of them used Siemens and Ferranti generators as their basis of study. William Stanley was quickly able to invent a better generator after being unsatisfied with the Siemens generator he used in his first experiment .

Above: Siemens AC generators used in London in 1885, in the US Edison was reluctant to jump into the AC power field while in Europe the technology was developing rapidly. 1886-1891 - Polyphase AC generators are developed by C.S. Bradly (US), August Haselwander (Germany), Mikhail Dolivo-Dobrovsky (Germany/Russia), Galileo Ferraris (Italy), and others. AC systems which include better control and powerful electric motors allow AC to compete. 1891 - Three-Phase AC power proves to be the best system for power generation and distribution at the International Electro-Technical Exhibition in Frankfurt. The three-phase generator designed by Mikhail Dolivo-Dobrovsky used at the exhibition is seen at left. 1892 - Charles P. Steinmetz presents his paper to the AIEE on hysteresis. Steinmetz's understanding of the mathematics of AC power is published and helps revolutionize AC power system design, including large AC Generators. 1890s - Generator design is improved rapidly thanks to commercial sales and available money for research.

Westinghouse, Siemens, Oerlikon, and General Electric develop the world's most powerful generators. Some generators still operate 115 years later. (Mechanicville, NY) Above: 1894 Elihu Thomson developed many AC generators for General Electric A later Westinghouse 2000 kW 270 Volt generator from after 1900 3. Videos

Question: Who discovered electromagnetic induction, so facilitating the transformer and dynamo?
Answer: Michael Faraday