Faraday, Michael (physicist)


(1791-1867) British Theoretical and Experimental Physicist (Electromagnetism), Physical Chemist

Michael Faraday was among the greatest 19th-century physicists to engage in the quest to understand electromagnetism and to harness electricity for human ends. His experimental work led him to discover electromagnetic induction and invent the electric motor, the electric generator, and the transformer. As a theorist, Faraday introduced the concept of force fields to explain the relationship of electricity and magnetism, replacing the time-honored idea of action at a distance. This new paradigm would dominate every aspect of modern physics.

Nothing in the circumstances of Michael Faraday’s birth, on September 22, 1791, in New-ington, Surrey, England, pointed to his illustrious future. His father, a poor blacksmith, would leave for London that same year to seek work. As a boy, Michael learned to read and write but was given little formal education and had a weak grounding in mathematics. When he was 14 he was apprenticed to a bookbinder and bookseller in London. It was there that his eclectic scientific training began. Encouraged to read, Michael devoured every book on science he could find in the shop and was soon performing his own crude experiments on electricity. Reading the works of the eminent French chemist Antoine Lavoisier sparked his fascination with chemistry. His bookbinding training helped him develop the manual dexterity that he would use to good purpose as an experimenter.

The young Faraday also took advantage of the educational opportunities London had to offer. In 1810, he was introduced to the City Philosophical Society, in which he received a basic education in science. He also began to attend the lecture series sponsored by the Royal Institution. In 1812, after listening to lectures presented by Sir Humphry Davy, the British chemist, Faraday managed to get himself hired as the great man’s laboratory assistant. The following year, he accompanied him to France and Italy, where he was exposed to the latest advances in scientific research and attended lectures by some of Europe’s most renowned researchers, including the pioneer of current electricity, alessandro guiseppe antonio anastasio volta.

When he returned to London Faraday embarked on a 20-year period at the Royal Institution when he would make most of his pioneering discoveries in electricity and chemistry. At the beginning he concentrated on chemistry, developing a method for liquefying chlorine and isolating benzene, a compound now widely used in chemical products. He combined his interests in chemistry and electricity in the study of electrolysis, the production of chemical change through certain conducting liquids, that is, electrolytes, and in 1834 formulated what became known as Faraday’s laws of electrolysis, which state that (1) the amount of chemical change produced is proportional to the charge passed, and (2) the amount of chemical change produced by a given charge depends on the ion concerned.

His great work in electromagnetism began in 1820, when the Danish physicist hans christian 0rsted discovered that a current in a wire deflects a magnetic needle. When Faraday repeated this experiment he found that a magnet also exerts a force on a wire carrying an electric current. Faraday explained the orientation of 0rsted’s compass by stating that circular lines of magnetic force are produced around the wire, a hypothesis he demonstrated by devising an apparatus that would cause a magnet to revolve around an electric current. In 1821, Faraday showed how electric and magnetic forces could be converted into mechanical motion by positioning a current-carrying wire between the north and south poles of a horseshoe magnet. The interaction of forces made the wire rotate, thus creating a simple electric motor. He demonstrated the following dynamics: (1) If a current flows in a wire close to a magnet that is not fastened down, the magnet moves. (2) If a current flows in a wire close to a magnet that is fastened down, the wire moves. By showing that either the conductor or the magnet could be made to move, Faraday had demonstrated with stunning simplicity that electrical energy could be converted into motive force.

Faraday’s fame grew, eventually eclipsing that of his mentor Davy, who felt that his own role in Faraday’s discoveries had been ignored. In 1824, he was elected as a member of the Royal Society, England’s premier scientific organization. The following year he began to popularize science through his lectures at the Royal Institution, an activity he would engage in throughout his career.

In 1831, Faraday embarked on the groundbreaking work that would lead him to the discovery of electromagnetic induction, that is, the production of electricity by means of varying magnetic intensity. He was not the first to demonstrate the phenomenon, but the first to understand its meaning. Seven years earlier, Frangois Arago had found that a rotating nonmagnetic copper disk caused the deflection of a magnetic needle placed above it. Nobody at the time could explain what was happening. Then Faraday performed the following experiment: using a ring of soft iron wrapped in two windings of insulated wire, he connected one wire to a galvanometer (which measures electric current) and the other to a battery. At first it appeared that nothing had happened. But when the circuit was broken and reconnected, the galvanometer recorded the pulse of an electric current. Faraday realized that an induced current was produced while the intensity of the magnetized iron ring was rising or falling: that is, a changing magnetic field can induce a current. (At the same time another American physicist, joseph henry, made the same discovery but could not spare time from his teaching to publish his findings.) The device Faraday constructed to demonstrate induction was the first transformer, or mechanism for changing the voltage supplied by an electrical current. Faraday made another great discovery when he realized that the motion of the copper wheel relative to the magnet in Arago’s experiment caused an electric current to flow in the disk, which in turn set up a magnetic field and deflected the magnet. He built a similar device in which the current produced could be led off; this was the first electric generator.

Throughout the 1830s Faraday’s string of discoveries showed no signs of abating. In 1832, he showed that the flow of electrostatic charge gives rise to the same effects as electric currents, thus proving that there is no basic difference between them. Then, in 1837, he investigated electrostatic force and demonstrated that it consists of a field of curved lines of force, and that different substances take up different amounts of electric charge when subjected to an electric field. This led Faraday to conceive of specific inductive capacity.

Faraday explained magnetism in terms of lines of force, which stretch out in all directions, flowing out of the north pole and into the south pole of a magnet. He knew little mathematics and found this concrete approach to the description of electricity and magnetism much more useful than the equations for the force between charges or currents in terms of an action at a distance. The field concept allowed the electric and magnetic forces to be clearly visualized and formed the basis for the mathematical description of electricity and magnetism, known today as electromagnetic theory.

Faraday suggested that the propagation of light through space consisted of vibrations in the field lines of electromagnetic force. He also found that when light passes through a medium, a magnetic field rotates the plane of polarization of the light. This is now known as the Faraday effect. His concepts of electric and magnetic fields were put into rigorous mathematical form a generation later by james clerk maxwell, who showed that light is, in fact, an oscillatory disturbance in the electromagnetic field lines, just as Faraday had predicted.

Another aspect of Faraday’s work, which illustrates his prescience, was his suggestion that a link between gravitation and electromag-netism may exist. Such a link was observed 70 years later in a test of albert einstein’s general theory of relativity, when light rays passing near the Sun were found to be deflected.

By 1850, Faraday’s years of brilliant scientific invention had ended. He abandoned research and then lecturing, retiring in 1858 on a small pension. Faraday was a deeply religious man, whose principles would not allow him to take part in preparation of poison gas for use in the Crimean War. Despite his fame, he remained modest, refusing to be knighted or receive honorary degrees. He died on August 25, 1867, in the Hampton Court apartment that had been given to him by Queen Victoria.

He is honored by the use of his name in the farad, the Systeme International d’Unites (SI) unit of capacitance, and the Faraday constant, the quantity of electricity needed to liberate a standard amount of substance in electrolysis.

Faraday’s extraordinary ability to visualize and pictorially represent physical processes underlay his discoveries of basic laws, which led directly to the age of electricity. His special genius enabled him to visualize not only his experimental apparatus (the coil and the magnet), but also the invisible field that surrounds it and conveys the electromagnetic force. His introduction of the concept of a field of force may well be his greatest contribution to modern science.

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