Year 13 visit to the Royal Institution

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Abbas, Sujeethan, Nicholas and Sarangan standing behind a statue of the great man, Michael Faraday

Introduction

I have been teaching electromagnetic induction to GCSE and A level students for well over twenty years now and it still amazes me that moving a piece of metal wire so that it cuts the magnetic field between a north and a south pole of magnets can be seen to produce and e.m.f or current if it is connected to a galvanometer or a sensitive ammeter/voltmeter.

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http://tap.iop.org/fields/electromagnetism/414/page_46948.html

You can get the same affect by moving a magnet back and forth through a coil of wire.

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In electromagnetic induction, e.m.f (or Electromotive force) can be defined around a closed loop as the electromagnetic work that would be transferred to a unit of charge if it travels once around that loop. Put simply it is the voltage developed by the movement of the magnet and/or the coil and is the basis of all the generators that can be found in our power stations or dynamos that we can use to light up the lamps on our bikes

The word “force” in this case is not used to mean mechanical force, measured in newtons, but a potential, or energy per unit of charge, measured in volts.

http://en.wikipedia.org/wiki/Electromotive_force

The e.m.f is induced if the coil or the magnet (or both) move.

The size of the induced emf depends on the speed of movement.

The direction of the induced emf depends on the direction of movement.

Changing the area or number of turns also changes the flux linkage, and so induces an emf. Flux linkage is equal to the product of the magnetic field (B), area of the coil (A) and the number of turns of wire of the coil(s) (N).

Flux linkage = BAN

It is just a term describing how much flux is linked by a loop or coil (i.e. how much is ‘caught’).

My students and I have access to very sensitive equipment and on a good day we can just about see this induced e.m.f. so what gave Michael Faraday the idea that this was a method of producing of electricity and how he was able to measure it given the equipment he had available is absolutely amazing.

Michael Faraday is a hero of mine. He achieved a great deal in his lifetime despite a very poor start.

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http://en.wikipedia.org/wiki/Michael_Faraday

He was born on the 22nd September 1791 in Newington Butts, England, which is now part of the London Borough of Southwark. He received very little formal education but made a point of educating himself. At fourteen he became an apprentice to George Riebau, a local bookbinder and bookseller in Blandford Street, London and during his seven-year apprenticeship he read many books, developing an interest in science, especially in electricity.

In 1812, at the age of twenty, and at the end of his apprenticeship, Faraday attended lectures by the eminent English chemist Humphry Davy of the Royal Institution and Royal Society. He subsequently sent Davy a three-hundred-page book based on notes that he had taken during these lectures. Davy’s reply was immediate, kind, and favourable and eventually appointed Faraday as Chemical Assistant at the Royal Institution on 1 March 1813.

Faraday is best known for his work regarding electricity and magnetism. In 1820 Hans Christian Ørsted (14 August 1777 – 9 March 1851), a Danish physicist had demonstrated the phenomenon of electromagnetism. He noticed a compass needle deflected from magnetic north when an electric current from a battery was switched on and off, confirming a direct relationship between electricity and magnetism and this led him showing that an electric current produces a circular magnetic field as it flows through a wire. Faraday went on to build two devices to produce what he called “electromagnetic rotation” using these ideas.

http://en.wikipedia.org/wiki/Hans_Christian_%C3%98rsted

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One of these, now known as the homopolar motor, caused a continuous circular motion that was produced by the circular magnetic force around a wire that extended into a pool of mercury in which was placed a magnet; the wire would then rotate around the magnet if supplied with current from a chemical battery.

Over the following years Faraday worked on other areas of science but continued with his experimental work on electromagnetism. In 1831 he began his great series of experiments in which he discovered electromagnetic induction, recording in his laboratory diary on 28 October 1831 he was; “making many experiments with the great magnet of the Royal Society”. His breakthrough came when he wrapped two insulated coils of wire around an iron ring, and found that upon passing a current through one coil a momentary current was induced in the other coil. This phenomenon is now known as mutual induction.

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In subsequent experiments, he found that if he moved a magnet through a loop of wire an electric current flowed in that wire. The current also flowed if the loop was moved over a stationary magnet. His demonstrations established that a changing magnetic field produces an electric field; this relation was modelled mathematically by James Clerk Maxwell as Faraday’s law, which subsequently became one of the four Maxwell equations, and which have in turn evolved into the generalisation known today as field theory.

http://en.wikipedia.org/wiki/James_Clerk_Maxwell

James Clerk Maxwell FRS FRSE (13 June 1831 – 5 November 1879) was a Scottish mathematical physicist, who became very good friends with Faraday although Faraday did bemoan the fact that Maxwell turned his work into a lot of mathematical equations that he couldn’t understand. Faraday was not a very good mathematician due his poor early education. As a physics undergraduate having to get to grips with Maxwell’s equations I have every sympathy with him.

Faraday would later use the principles he had discovered to construct the electric dynamo, the ancestor of modern power generators and the electric motor.

Near the end of his career, Faraday proposed that electromagnetic forces extended into the empty space around the conductor. This idea was rejected by his fellow scientists, and Faraday did not live to see the eventual acceptance of his proposition by the scientific community. Faraday’s concept of lines of flux emanating from charged bodies and magnets provided a way to visualise electric and magnetic fields; that conceptual model was crucial for the successful development of the electromechanical devices that dominated engineering and industry for the remainder of the 19th century.

http://www.rigb.org/our-history/michael-faraday

Because Michael Faraday is very closely associated with the Royal Institution you can find out a lot about him there. You can also see some of the equipment he used.

http://www.rigb.org/our-history/michael-faraday/magnetic-laboratory

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Faraday’s homopolar generator and giant electromagnet

http://en.wikipedia.org/wiki/Homopolar_generator

Michael Faraday used the electromagnet shown below to show that light and glass are affected by magnetism. He was determined to prove that all matter is magnetic, and that electricity, magnetism and light are similar kinds of phenomenon. He placed a dense piece of glass on the poles of the electromagnet, and then passed polarised light through it. When he turned on the electric current, the polarisation of the light changed, confirming that both light and glass possessed magnetic properties.

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During the 1820s Faraday sought to discover how to make electricity from magnetism. He achieved success with the device pictured below

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The above images show some of Faraday’s insulated iron rings. The one of the right was actually used by Faraday to discover electromagnetic induction on the 29th August 1831. His great insight was that induction produced a transient electrical current, not a continuous one. This device is the first transformer and so is the basis of modern electrical technology.

The rings are made from everyday materials such as wire made for bonnets, although the iron ring on the right seems to have been specially made.

Making the induction ring was a tedious process since Faraday had to wind the coils of wire on opposite sides of the ring and insulate them with cotton. He doesn’t mention the time taken in his diary but it was probably about ten working days.

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http://www.rigb.org/docs/faraday_notebooks__induction_0.pdf

When he passed an electric current through one coil he induced an electric current in the other coil, which flowed for a very brief period of time.

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The above images show the electric generators that Faraday created on the 17th October 1831. He generated electricity by pushing and pulling a magnet through the coil of wire.

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This is Michael Faraday’s generator. This apparatus consists of a tube of neutral material wound with a coil of wire, insulated in cotton, and a bar magnet.

Ten years after Faraday created the electric motor he returned to his electrical research and discovered electro-magnetic induction in August 1831. A few months later he successfully conducted an experiment using this apparatus and demonstrated the relationship between magnetism and motion.

Faraday connected his apparatus to a galvanometer (an instrument that detects electrical current) and discovered that when he passed the magnet back and forth through the coil of wire, which remained stationary, the needle of the galvanometer leapt into action registering a current flowing.

As the magnet moves the lines of magnetic force repeatedly intersect with the wire exciting the electrons in the wire and generating electrical current. So if you exchanged the galvanometer with a light bulb today you would see it light up.

Virtually all electric power is produced using Faraday’s principles, no matter whether the prime source of energy is coal, oil, gas, nuclear, hydro, or wind: all these fuels are used to drive a generator (or turbine) which generates the electrical current.

http://www.rigb.org/docs/faraday_notebooks__generator_0.pdf

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The above images show a sample of the many coils that Faraday made and used in his experiments. Insulated wire was not available in 1831 so he insulated his wire with string. The process was very time consuming and one of the rings took 10 days to make.

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The images below show excerpts form Faraday’s own notebook

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Michael Faraday’s Use of Mercury by Nicholas Savva 13I

The royal institution visit was a good opportunity to see all of the equipment Michael Faraday used in his experiments about electricity and magnetism. What was rather interesting was that he used a bowl of mercury to show that a magnetic compass needle could be caused to move by a wire carrying an electric current.

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Photo Credits: Paul Wilkinson

Materials: Glass, wood, copper, iron, wax, mercury

Measurements – H: 247mm, W: 173mm, D: 121mm

Key words: Magnetic rotation

Faraday also used this mercury bath to transform electrical energy into mechanical energy, creating the first electric motor.

This simple looking object was made by Michael Faraday in 1822. Its simplicity masks its true importance as the first surviving electric motor.

In 1820 Hans Christian Ørsted announced his discovery that the flow of an electric current through a wire produced a magnetic field around the wire. André-Marie Ampère followed on and showed that the magnetic force apparently was a circular one, producing in effect a cylinder of magnetism around the wire. No such circular force had ever before been observed.

Self-taught British scientist Michael Faraday (1791 – 1867) was the first to understand what these discoveries implied. If a magnetic pole could be isolated, it ought to move constantly in a circle around a current-carrying wire.

In 1821 Faraday set about trying to understand the work of Ørsted and Ampère, devising his own experiment using a small mercury bath. This device, which transformed electrical energy into mechanical energy, was the first electric motor.

This apparatus is the only original surviving example made by Faraday the following year after his discovery in 1822.

The motor features a stiff wire which hang down into a glass vessel which has a bar magnet secured at the bottom. The glass vessel would then be part filled with mercury (a metal that is liquid at room temperature and an excellent conductor). Faraday connected his apparatus to a battery, which sent electricity through the wire creating a magnetic field around it. This field interacted with the field around the magnet and caused the wire to rotate clockwise.

This discovery led Faraday to contemplate the nature of electricity. Unlike his contemporaries, he was not convinced that electricity was a material fluid that flowed through wires like water through a pipe. Instead, he thought of it as a vibration or force that was somehow transmitted as the result of tensions created in the conductor.

This object is currently on display in Faraday’s original magnetic laboratory in the Faraday Museum at the Royal Institution.

http://www.rigb.org/our-history/iconic-objects/iconic-objects-list/faradays-motor

Mercury is a very dangerous element to work with so working with it, without wearing any protection must have been a health risk.”

http://www.scs.illinois.edu/~mainzv/HIST/bulletin_open_access/num11/num11%20p47-50.pdf

Michael Faraday did have health problems corresponding to the symptoms of mercury poisoning and in 1840 he had to stop his scientific work and take an extended holiday.

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