Faraday's greatest work probably was with electricity and magnetism. The first experiment which he recorded was the construction of a
voltaic pile with seven halfpence pieces, stacked together with seven disks of sheet zinc, and six pieces of paper moistened with salt water. With this pile he decomposed sulphate of magnesia (first letter to Abbott,
July 12, 1812).
In
1821, soon after the Danish physicist and chemist,
Hans Christian Ørsted discovered the phenomenon of
electromagnetism, Davy and British scientist
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: a continuous circular motion from the circular magnetic force around a wire and a wire extending into a pool of
mercury with a magnet placed inside would rotate around the magnet if supplied with current from a chemical battery. The latter device is known as a
homopolar motor. These experiments and inventions form the foundation of modern electromagnetic technology. 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.
At this stage, there is also evidence to suggest that Davy may have been trying to slow Faraday’s rise as a scientist (or natural philosopher as it was known then). In 1825, for instance, Davy set him onto optical glass experiments, which progressed for six years with no great results. It was not until Davy's death, in 1829, that Faraday stopped these fruitless tasks and moved on to endeavors that were more worthwhile. Two years later, in
1831, he began his great series of experiments in which he discovered
electromagnetic induction. (
Joseph Henry likely discovered
self-induction a few months earlier and both may have been anticipated by the work of
Francesco Zantedeschi in Italy in 1829 and 1830.
Faraday's breakthrough came when he wrapped two insulated coils of wire around a massive iron ring, bolted to a chair, and found that upon passing a current through one coil, a momentary current was induced in the other coil. This phenomenon is known as
mutual induction. The iron ring-coil apparatus is still on display at the Royal Institution. In subsequent experiments 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. His demonstrations established that a changing magnetic field produces an electric field. This relation was mathematically modelled by
Faraday's law, which subsequently became one of the four
Maxwell equations. These in turn have evolved into the generalization known today as
field theory.
Faraday later used the principle to construct the electric
dynamo, the ancestor of modern power generators.
In
1839 he completed a series of experiments aimed at investigating the fundamental nature of electricity. Faraday used "
static", batteries, and "
animal electricity" to produce the phenomena of electrostatic attraction,
electrolysis, magnetism, etc. He concluded that, contrary to scientific opinion of the time, the divisions between the various "kinds" of electricity were illusory. Faraday instead proposed that only a single "electricity" exists, and the changing values of quantity and intensity (voltage and charge) would produce different groups of phenomena.
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 this idea eventually accepted. Faraday's concept of lines of flux emanating from charged bodies and magnets provided a way to visualize electric and magnetic fields. That mental model was crucial to the successful development of electromechanical devices which dominated engineering and industry for the remainder of the 19th century.
In 1845 he discovered the phenomenon that he named
diamagnetism, and what is now called the
Faraday effect: 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.
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.
Faraday was an excellent experimentalist who conveyed his ideas in clear and simple language. However, his mathematical abilities did not extend as far as trigonometry or any but the simplest algebra. It was
James Clerk Maxwell who took the work of Faraday, and others, and consolidated it with a set of equations that lie at the base of all modern theories of electromagnetic phenomena.
rss feed