Faraday and his law of induction

Michael Faraday’s knowledge of mathematics was limited to elementary algebra, but he was a brilliant experimenter, able to draw conclusions from his laboratory work and to communicate them to colleagues and the general public.

He began his career as a laboratory assistant to the renowned chemist Humphry Davy. In early years, he focused on chemistry, discovering new carbon chlorides and successfully liquefying chlorine and other gases. In 1825 he isolated benzene. In the years that followed, Faraday turned his attention to electricity and magnetism, building on the works of Charles Coulomb, Hans Christian Ørsted and André-Marie Ampère.

He was a relentless experimenter and always kept careful records, an approach that was highly successful for him. Faraday’s law says that the induced electromotive force in any closed circuit is equal to the negative of the time-rate-of-change of the magnetic flux enclosed by the circuit. Committed to the idea of conservation of energy, Faraday reasoned that because an electric current could give rise to a magnetic field, the reverse must be true. In 1831, he built a device that demonstrated that a magnetic field could induce current to flow in a nearby conductor. This insight laid the groundwork for the invention of the dynamo, which produces large amounts of usable electricity by means of the relative motion of a magnetic field and a conductor. It remained for a later theoretician, James Clerk Maxwell, to mathematize this concept pioneered by Faraday.

Another of Faraday’s formidable discoveries, announced in 1845, was that a magnetic field can rotate a beam of polarized light. Besides preparing the way for a great many subsequent developments including the flat-screen TV and oscilloscopes, this discovery gave rise to the revolutionary insight that light and similar forms of radiation are actually electromagnetic phenomena.

In addition to being a brilliant experimenter who was quick to draw conclusions from his observations, Faraday had a gift for communicating his insights to the public. In later years he lectured widely, including to audiences of children, whom he delighted with spirited and sometimes humorous talks based upon his momentous discoveries.

To honor him the SI notation system denotes the basic unit of capacitance as a farad, the ability of a body to store electrical charge. One farad is the amount of capacitance across a capacitor charged with one coulomb of electrical energy when there is a potential of one volt between the plates. A farad is a large amount of capacitance, so we generally characterize most working capacitive circuit elements in microfarads.