Faraday, Michael (1791–1867)

A portrait of the English chemist and physicist Michael Faraday. He began his working life apprenticed to a bookbinder, but at the age of 21 he started researching electricity. He took a job at the Royal Institution of Great Britain a year later, and by 1833 had succeeded Humphry Davy as professor of chemistry there. He is regarded as the founder of electrochemistry.

English physicist and chemist Michael Faraday, one of the most prominent experimentalists of the 19th century. Largely self-educated, Faraday is best known for his discoveries about the relationship between electricity and magnetism, published in the series Experimental Researches on Electricity (1839–55), which formed the basis of the theory of electromagnetic behaviour.

English chemist and physicist. In 1821 he began experimenting with electromagnetism, and discovered electromagnetic induction (the production of a continuous supply of electricity using magnetic fields). He made the first dynamo, the first electric motor, the first transformer, and developed the first electric generator. He also pointed out that the energy of a magnet is in the field around it and not in the magnet itself. In chemistry, Faraday isolated benzene from gas oils, demonstrated the use of platinum as a catalyst, and developed the laws of electrolysis in 1834.

Faraday created the technique and apparatus used for electrolysis (the production of chemical changes by passing electric current through an aqueous solution), and coined the terms anode, cathode, cation, anion, electrode, and electrolyte.

In 1846 he carried out work on polarized light. Using powerful electromagnetism Faraday was able to show that the electromagnetic field could change the plane of polarization in the light to rotate. The greater the strength of the magnetic field, the greater the angle of rotation in the plane of polarization. Faraday also worked on the different responses of substances to a magnetic field, describing objects that were attracted as paramagnetic, and objects that were repulsed as diamagnetic.

Faraday was born in Newington, Surrey, the son of a blacksmith. He was apprenticed to a London bookbinder, and was largely self-educated. In 1812, he began researches into electricity, and made his first electrical cell. Faraday's mentor was the chemist Humphry Davy, whom he first saw give a lecture in 1812. He became a laboratory assistant to Davy at the Royal Institution in 1813, and worked with him during a tour of Europe's cities and universities. Faraday became a member of the Royal Society from 1820, and in 1827 succeeded Davy as professor of chemistry at the Royal Institution. Faraday delivered highly popular lectures at the Royal Institution between 1825 and 1862. He was deeply religious, and refused to take part in the preparation of poison gas for use in the Crimean War.

Chemistry and the discovery of benzene Faraday was mainly interested in chemistry during his early years at the Royal Institution. He investigated the effects of including precious metals in steel in 1818, producing high-quality alloys that later encouraged the production of special high-grade steels. In 1823 Faraday produced liquid chlorine by heating crystals of chlorine hydrate in an inverted U-tube, one end of which was heated and the other placed in a freezing mixture. After the production of liquid carbon dioxide in 1835, he used this coolant to liquefy other gases. In the same year, Faraday isolated benzene from gas oils and demonstrated the use of platinum as a catalyst. He also demonstrated the importance in chemical reactions of surfaces and inhibitors, foreshadowing a huge area of the modern chemical industry.

Laws of electrolysis Faraday's laws of electrolysis established the link between electricity and chemical affinity, one of the most fundamental concepts in science. Electrolysis is the production of chemical changes by passing an electric current through a solution. He suggested the theory that, during the electrolysis of an aqueous (water-based) electrolyte, positively charged cations move towards the negatively charged cathode and negatively charged anions migrate to the positively charged anode. Faraday demonstrated that the ions are discharged at each electrode according to the following rules:

(a) the quantity of a substance produced is proportional to the amount of electricity passed;

(b) the relative quantities of different substances produced by the same amount of electricity are proportional to their equivalent weights (that is, the relative atomic mass divided by the oxidation state or valency).

Electromagnetism and the electric motor In 1821, only one year after Danish physicist Hans Oersted had discovered with a compass needle that a current of electricity flowing through a wire produces a magnetic field, Faraday was asked to investigate the phenomenon of electromagnetism by the editor of the Philosophical Magazine. Faraday decided that circular lines of magnetic force were produced around the wire, thus explaining the orientation of Oersted's compass needle.

Faraday's conviction that an electric current gives rise to lines of magnetic force arose from his idea that electricity was a form of vibration and not a moving fluid. He believed that electricity was a state of varying strain in the molecules of the wire conductor, and that this gave rise to a similar strain in the medium surrounding the conductor. It was reasonable to consider therefore that the transmitted strain might set up a similar strain in the molecules of another nearby conductor.

Faraday set about devising an apparatus that would demonstrate the conversion of electrical energy into motive force. His device consisted of two vessels of mercury connected to a battery. Above the vessels and connected to each other were suspended a magnet and a wire, which were free to move and dipped just below the surface of the mercury. In the mercury were fixed a wire and a magnet respectively. When the current was switched on, it flowed through both the fixed and free wires, generating a magnetic field in them. This caused the free magnet to revolve around the fixed wire, and the free wire to revolve around the fixed magnet.

The experiment demonstrated the basic principles governing the electric motor. Although the practical motors that were later developed had a very different form to Faraday's apparatus, he is usually credited with the invention of the electric motor.

Electromagnetic induction and the transformer Faraday hunted for the effect of electromagnetic induction from 1824 onwards, expecting to find that a magnetic field would induce a steady electric current in a conductor. Faraday eventually succeeded in producing induction in 1831. He wound two coils around an iron bar and connected one to a battery and the other to a galvanometer (an instrument for detecting small electric currents by their magnetic effect). Nothing happened when the current flowed through the first coil, but Faraday noticed that the galvanometer responded whenever the current was switched on or off. Faraday found an immediate explanation with his lines of force. If the lines of force were cut – that is, if the magnetic field changed – then an electric current would be induced in a conductor placed within the magnetic field. The iron bar helped to concentrate the magnetic field, as Faraday later came to understand, and a current was induced in the second coil by the magnetic field momentarily set up as current entered or left the first coil. With this device, Faraday had discovered the transformer, a modern transformer being no different in essence even though the alternating current required had not then been discovered.

Faraday is thus also credited with the simultaneous discovery of electromagnetic induction, although the same discovery had been made in the same way by US physicist Joseph Henry in 1830. However, Henry had not been able to publish his findings before Faraday did, although both men are now credited with the independent discovery of induction.

Arago's wheel and the electric generator In 1824 the French physicist Francois Arago found that a rotating nonmagnetic disc, specifically of copper, caused the deflection of a magnetic needle placed above it. This was in fact a demonstration of electromagnetic induction, but nobody at that time could explain ‘Arago's wheel’. Faraday realized that the motion of the copper wheel relative to the magnet in Arago's experiment caused an electric current to flow in the disc, which in turn set up a magnetic field and deflected the magnet. He set about constructing a similar device in which the current produced could be led off, and built the first electric generator in 1831. It consisted of a copper disc that was rotated between the poles of a magnet; Faraday touched wires to the edge and centre of the disc and connected them to a galvanometer, which registered a steady current.

Electrostatic charge In 1832 Faraday showed that an electrostatic charge gives rise to the same effects as current electricity. He demonstrated in 1837 that electrostatic force consists of a field of curved lines of force, and that different substances have specific inductive capacities – that is, they take up different amounts of electric charge when subjected to an electric field.

In 1838 he proposed a theory of electricity elaborating his idea of varying strain in molecules. In a good conductor, a rapid build-up and breakdown of strain took place, transferring energy quickly from one molecule to the next. This also accounted for the decomposition of compounds in electrolysis. At the same time, Faraday wrongly rejected the notion that electricity involved the movement of any kind of electrical fluid (the motion of electrons is involved). However, Faraday's theory that this motion causes a rapid transfer of electrical energy through a conductor was correct.

Polarization of light Finally, Faraday considered the nature of light and in 1846 arrived at a form of the electromagnetic theory of light that was later developed by Scottish physicist James Clerk Maxwell. In 1845 Lord Kelvin suggested that Faraday investigate the action of electricity on polarized light. Faraday had in fact already carried out such experiments with no success, but this could have been because the electrical forces were not strong. Faraday now used an electromagnet to give a strong magnetic field instead and found that it causes the plane of polarization to rotate, the angle of rotation being proportional to the strength of the magnetic field.

Paramagnetism and diamagnetism Several further discoveries resulted from this experiment. Faraday realized that the glass block used to transmit the beam of light must also transmit the magnetic field, and he noticed that the glass tended to set itself at right-angles to the poles of the magnet rather than lining up with it as an iron bar would. He showed that the differing responses of substances to a magnetic field depended on the distribution of the lines of force through them. He called materials that are attracted to a magnetic field paramagnetic, and those that are repulsed diamagnetic. Faraday then went on to point out that the energy of a magnet is in the field around it and not in the magnet itself, and he extended this basic conception of field theory to electrical and gravitational systems.

Although Faraday's work in chemistry was significant, he is most remembered for his work on electricity. During his lifetime his electromagnetic work was put to groundbreaking use in communications. In 1835 US inventor Samuel Morse invented the first adequate electric telegraph and in 1837 British inventors William Cooke and Charles Wheatstone patented a railway telegraph; Morse later developed the Morse code. Telegraphy systems required the use of electric power and technology for transmission. Indeed, although it came nine years after his death, the invention of the telephone by Scottish-born US scientist Alexander Graham Bell relied on Faraday's work as the basis of its mechanisms. Faraday's findings concerning the electromagnetic properties of light eventually led to the invention and successful trial of radio communications in 1901 by the Italian engineer Guglielmo Marconi.