Timeline of Electricity and Magnetism

The fields of electricity and magnetism are intimately intertwined. However, humankind’s knowledge of magnetism and static electricity began more than 2,000 years before they were first recognized to be separate (though interrelated) phenomena. Once that intellectual threshold was crossed – in 1551 – scientists took more bold steps forward (and more than a few steps back) toward better understanding and harnessing these forces. The next 400 years would see a succession of discoveries that advanced our knowledge of magnetism, electricity and the interplay between them, leading to ever more powerful insights and revolutionary inventions.

This timeline highlights important events and developments in these fields from prehistory to the beginning of the 21st century. It also includes related developments in other disciplines (such as the evolution of computers).

600 BC - 1599 – Humans discover the magnetic lodestone as well as the attracting properties of amber. Advanced societies, in particular the Chinese and the Europeans, exploit the properties of magnets in compasses, a tool that makes possible exploration of the seas, “new worlds” and the nature of Earth’s magnetic poles.

1600 - 1699 – The Scientific Revolution takes hold, facilitating the groundbreaking work of luminaries such as William Gilbert, who took the first truly scientific approach to the study of magnetism and electricity and wrote extensively of his findings.

1700 - 1749 – Aided by tools such as static electricity machines and Leyden jars, scientists continue their experiments into the fundamentals of magnetism and electricity.

1750 - 1774 – With his famous kite experiment and other forays into science, Benjamin Franklin advances knowledge of electricity, inspiring his English friend Joseph Priestley to do the same.

1775 - 1799 – Scientists take important steps toward a fuller understanding of electricity, as well as some fruitful missteps, including an elaborate but incorrect theory on animal magnetism that sets the stage for a groundbreaking invention.

1800 - 1819 – Alessandro Volta invents the first primitive battery, discovering that electricity can be generated through chemical processes; scientists quickly seize on the new tool to invent electric lighting. Meanwhile, a profound insight into the relationship between electricity and magnetism goes largely unnoticed.

1820 - 1829 – Hans Christian Ørsted’s accidental discovery that an electrical current moves a compass needle rocks the scientific world; a spate of experiments follows, immediately leading to the first electromagnet and electric motor.

1830 - 1839 – The first telegraphs are constructed and Michael Faraday produces much of his brilliant and enduring research into electricity and magnetism, inventing the first primitive transformer and generator.

1840 - 1849 – The legendary Faraday forges on with his prolific research and the telegraph reaches a milestone when a message is sent between Washington, DC, and Baltimore, MD.

1850 - 1869 – The Industrial Revolution is in full force, Gramme invents his dynamo and James Clerk Maxwell formulates his series of equations on electrodynamics.

1870 - 1879 – The telephone and first practical incandescent light bulb are invented while the word “electron” enters the scientific lexicon.

1880 - 1889 – Nikola Tesla and Thomas Edison duke it out over the best way to transmit electricity and Heinrich Hertz is the first person (unbeknownst to him) to broadcast and receive radio waves.

1890 - 1899 – Scientists discover and probe x-rays and radioactivity, while inventors compete to build the first radio.

1900 - 1909 – Albert Einstein publishes his special theory of relativity and his theory on the quantum nature of light, which he identified as both a particle and a wave. With ever new appliances, electricity begins to transform everyday life.

1910 - 1929 – Scientists’ understanding of the structure of the atom and of its component particles grows, the phone and radio become common, and the modern television is born.

1930 - 1939 – New tools such as special microscopes and the cyclotron take research to higher levels, while average citizens enjoy novel amenities such as the FM radio.

1940 - 1959 – Defense-related research leads to the computer, the world enters the atomic age and TV conquers America.

1960 - 1979 – Computers evolve into PCs, researchers discover one new subatomic particle after another and the space age gives our psyches and science a new context.

1980 - 2003 – Scientists explore new energy sources, the World Wide Web spins a vast network and nanotechnology is born.

Pioneers in Electricity and Magnetism

Ampere, Celsius, Kelvin, Hertz, Tesla: These terms are familiar to all science students. Behind them is a group of scientists who went down in history for their groundbreaking work in magnetism and electricity. Who were these brilliant inventors, physicists and chemists, and what lasting contributions did they make to their fields - and to our lives? Get to know these pioneers by visiting the individual pages below, which are hosted on our sister site at the National High Magnetic Field Laboratory in Tallahassee, Florida.

André-Marie Ampère (1775-1836) – Although he was not the first person to observe a connection between electricity and magnetism,

André-Marie Ampère was the first scientist to attempt to theoretically explain and mathematically describe the phenomenon. His contributions laid the groundwork upon which the science of electrodynamics (a term coined by Ampère, but now more commonly referred to as electromagnetics) has been built.

Svante Arrhenius (1859-1927) – Svante Arrhenius was born in Vik, Sweden, and became the first native of that country to win the Nobel

Prize. The award for chemistry was bestowed to him in honor of his theory of electrolytic dissociation. In its incipient form, which appeared in his

doctoral dissertation, the theory was poorly received by his professors. The barely passing grade that he was given for the dissertation did not discourage Arrhenius, however, and his persistence eventually led to the general acceptance of many of his ideas regarding electrolytes, acids, bases and chemical reactions.

John Bardeen (1908-1991) – John Bardeen was one of a handful of individuals awarded the Nobel Prize twice and the first scientist to win

dual awards in physics. Both times, he shared the prize with others. The first time his co-recipients were Walter Brattain and William Shockley, who combined their efforts with Brattain in the invention of the transistor. The second time he shared the prize with Leon Cooper and Robert Schrieffer, with whom he developed the first generally accepted theory of low-temperature superconductivity.

Georg Bednorz (1950-Present) – J. Georg Bednorz jointly revolutionized superconductivity research with K. Alex Müller by

discovering an entirely new class of superconductors, often referred to as high-temperature superconductors. Since Heike Kamerlingh Onnes discovered superconductivity in 1911, all superconductors known up until the time of the Bednorz and Müller discovery lost their electrical resistance and entered the superconducting state at temperatures barely above absolute zero. These early superconductors were made of metals or semiconducting alloys, but Bednorz and Müller managed to achieve superconductivity at temperatures higher than any previously possible by using ceramics made from metallic oxide mixtures.

Gerd Binnig (1947-Present) – A native of Germany, the physicist Gerd Binnig co-developed the scanning tunneling

microscope (STM) with Heinrich Rohrer while the pair worked together at the IBM Research Laboratory in Switzerland. The invention of the STM allowed scientists entry into the atomic world in a new way and was a major advance in the field of nanotechnology. For their remarkable achievement, Binnig and Rohrer shared the 1986 Nobel Prize in Physics with Ernst Ruska, inventor of the electron microscope. That same year Binnig

developed the first atomic force microscope (AFM), further expanding the array of tools available to researchers seeking a better understanding of materials on an atomic scale.

Felix Bloch (1905-1983) – Physicist Felix Bloch developed a non-destructive technique for precisely observing and measuring the

magnetic properties of nuclear particles. He called his technique “nuclear induction,” but nuclear magnetic resonance (NMR) soon became the preferred term for the method, which was a notable advance upon an earlier technique developed by Isidor Rabi. Bloch received half of the Nobel Prize in Physics in 1952 for this work, sharing the award with Edward Purcell, who independently developed a similar method of achieving and detecting nuclear magnetic resonance at approximately the same time. NMR is the basis of an important medical imaging technique, magnetic resonance imaging (MRI).

Walter Brattain (1902-1987) – Walter Houser Brattain discovered the photo-effect that occurs at the free surface of a semiconductor

and was co-creator of the point-contact transistor, which paved the way for the more advanced types of transistors that eventually replaced vacuum tubes in almost all electronic devices in the latter half of the twentieth century. The invention of the transistor took place at Bell Labs, where Brattain worked closely with John Bardeen as part of the solid-state physics group headed by William Shockley. Brattain, Bardeen and Shockley shared the Nobel Prize in Physics in 1956 for their combined efforts in the development of the transistor.

Anders Celsius (1701-1744) – Anders Celsius is most familiar as the inventor of the temperature scale that bears his name. The

Swedish astronomer, however, also is notable as the first person to make a connection between the radiant atmospheric phenomenon known as the aurora borealis, or the northern lights, and the magnetic field of the Earth. He published his studies of the aurora borealis, including his accurate speculation regarding its relation to magnetism, in 1733.

Leon Cooper (1930-Present) – Leon Cooper shared the 1972 Nobel Prize in Physics with John Bardeen and Robert Schrieffer, with whom

he developed the first widely accepted theory of superconductivity. Termed the BCS theory, it is heavily based on a phenomenon known as Cooper pairing. According to the theory, the electrons in a superconducting material form associated pairs that together act as a single system. Unless the movement of all pairs is halted simultaneously, the current flowing through a superconductor meets no resistance, and will continue ad infinitum.

Charles-Augustin de Coulomb (1736-1806) – Charles-Augustin de Coulomb invented a device, dubbed the torsion balance, that

allowed him to measure very small charges and experimentally estimate the force of attraction or repulsion between two charged bodies. The data he obtained through his extensive use of the torsion balance enabled Coulomb to formulate one of the fundamental laws of electromagnetism, which bears his name (Coulomb’s law).

William Crookes (1832-1919) – English scientist William Crookes was very innovative in his investigations with vacuum tubes and

designed a variety of different types to be used in his experimental work. Crookes tubes are glass vacuum chambers that contain a positive electrode (anode) and a negative electrode (cathode). When an electrical current is passed between the electrodes of one of the tubes, a glow can be seen in the chamber. Crookes also discovered the element Thallium.

Humphry Davy (1778-1829) – Humphry Davy was a pioneer in the field of electrochemistry who used electrolysis to isolate many

elements from the compounds in which they occur naturally. Electrolysis is the process by which an electrolyte is altered or decomposed via the application of an electric current. In addition to his isolation of sodium, potassium and other alkaline earth metals, electrolysis enabled Davy to

disprove the view proposed by French chemist Antoine-Laurent Lavoisier that oxygen was an essential component of all acids.

Peter Debye (1884-1966) – Peter Debye carried out pioneering studies of molecular dipole moments, formulated theories of

magnetic cooling and of electrolytic dissociation, and developed an X-ray diffraction technique for use with powdered, rather than crystallized, substances. For his work with dipole moments, the vector quantities related to the distribution of electric charges are measured indebyes. Also, in recognition of a number of his scientific contributions, Debye received the Nobel Prize in Chemistry in 1936.

Lee De Forest (1873-1961) – American inventor Lee De Forest was a pioneer of radio and motion pictures. He received more than 300

patents over the course of his lifetime, the most important of which was for a three-electrode vacuum tube, or triode, that he called the Audion. The invention of the Audion, a device capable of amplifying and modulating electromagnetic signals that could also function as an oscillator, was a crucial step in the early electronics industry. Until the invention of the transistor in 1948, the triode was featured in almost all electronic equipment.

Paul A. M. Dirac (1902-1984) – Paul Adrien Maurice Dirac was an outstanding twentieth century theoretical physicist whose work was

fundamental to the development of quantum mechanics and quantum electrodynamics. He was awarded the Nobel Prize for Physics jointly with Erwin Schrödinger in 1933 for his contributions to atomic theory, Dirac’s prediction of the existence of antimatterhaving been experimentally proven by that time.

Willem Einthoven (1860-1927) – Willem Einthoven invented a string galvanometer that could be used to directly record the electrical

activity of the heart. The investigations he carried out with the device

enabled him to determine that graphical recordings of heart activity, or electrocardiograms as they came to be known, generally conform to a basic type, that individuals produce their own characteristic electrocardiograms typically conforming to this type, and that deviations are often associated with heart disease. For his discovery of the mechanism of the electrocardiogram, Einthoven was awarded the Nobel Prize in Physiology or Medicine in 1924.

Roland Eötvös (1848-1919) – Vásárosnaményi Báró Eötvös Loránd, better known as Roland EEötvös or Loránd Eötvös throughout much

of the world, was a Hungarian physicist who is most recognized for his extensive experimental work involving gravity, but who also made significant studies of capillarity and magnetism. He employed an instrument of his own design commonly referred to as the Eötvös balance to make extensive measurements, ultimately demonstrating to a much higher degree of accuracy than had been ever achieved before that gravitational mass and inertial mass are equivalent.

Enrico Fermi (1901-1954) – Enrico Fermi was a titan of twentieth-century physics. Adept in both theory and experiment, the Italian-

born American outlined the statistical laws that govern the behavior of particles that abide by the Pauli exclusion principle and developed a theoretical model of the atom when he was only in his mid-twenties. He went on to incorporate the neutral particle (lightheartedly hailed by Fermi as the neutrino, or “little neutral one”) hypothesized by Wolfgang Pauli into a quantitative theory of beta decay, as well as to demonstrate that bombardment of elements with neutrons can generate artificial radioactivity and that slow neutrons produce much Ber nuclear reactions. These latter discoveries paved the way for invention of nuclear reactors and the atomic bomb.

Richard Feynman (1918-1988) – Theoretical physicist Richard Phillips Feynman greatly simplified the way in which the interactions

of particles could be described through his introduction of the diagrams that now bear his name (Feynman diagrams) and was a co-recipient of the

Nobel Prize in Physics in 1965 for his reworking of quantum electrodynamics (QED). He is often remembered as much for his offbeat personality and lively wit as for his considerable contributions to twentieth-century physics.

John Ambrose Fleming (1849-1945) – John Ambrose Fleming was an electronics pioneer who invented the oscillation valve, or

vacuum tube, a device that would help make radios, televisions, telephones and even early electronic computers possible. A brilliant innovator, Fleming was particularly adept at solving technical problems, and at various times in his life he was closely acquainted with James Clerk Maxwell, Thomas Edison and Guglielmo Marconi. He taught at University College, London, for many years and is often credited with devising the right-hand rule to help his students easily determine the directional relationships between a current, its magnetic field and electromotive force.

Luigi Galvani (1737-1798) – Luigi Galvani was a pioneer in the field of electrophysiology, the branch of science concerned with electrical

phenomena in the body. His experiments with dissected frogs and electrical charges led him to suggest the existence of a previously unknown type of electricity, which he dubbedanimal electricity. Galvani’s explanation of his experimental findings was controversial and inspired Alessandro Volta to develop an alternate viewpoint as well as to invent the voltaic pile.

Carl Friedrich Gauss (1777-1853) – Although he is best known as one of the greatest mathematicians of all time, Carl Friedrich Gauss

was also a pioneer in the study of magnetism and electricity. To facilitate an extensive survey of terrestrial magnetism, he invented an early type of magnetometer, which is a device capable of measuring the direction and strength of a magnetic field. Gauss also developed a consistent system of magnetic units and with Wilhelm Weber built one of the first electromagnetic telegraphs. Gauss’s laws describing magnetic and electric fluxes served as part of the foundation upon which James Clerk Maxwell developed his famous equations and electromagnetic theory.

Murray Gell-Mann (1929-Present) – Murray Gell-Mann is a theoretical physicist who won the Nobel Prize for Physics in 1969 for

his contributions to elementary particle physics. He is particularly well known for his role in bringing organization into the world of subatomic particles, which before his work seemed to be verging on chaos, and for developing the concept of quarks. In the latter part of his career his focus has shifted from the most basic aspects of nature to complex adaptive systems, which he currently explores at the Santa Fe Institute.

William Gilbert (1544-1603) – William Gilbert was an English physician and natural philosopher who wrote a six-volume treatise

that compiled all of the information regarding magnetism and electricity known at the time. Entitled De Magnete, Magneticisque Corporibus, et de Magno Magnete Tellure (On the Magnet, Magnetic Bodies, and the Great Magnet of the Earth), the work included descriptions of many of Gilbert’s own experiments and the conclusions he drew from them, as well as data that had been previously obtained by others. In this opus, Gilbert established much of the basic terminology still employed in the field of electromagnetics, including electricity, electric attraction and force and magnetic pole.

Joseph Henry (1797-1878) – Joseph Henry was an American scientist who pioneered the construction of B, practical

electromagnets and built one of the first electromagnetic motors. During his experiments with electromagnetism, Henry discovered the property of inductance in electrical circuits, which was first recognized at about the same time in England by Michael Faraday, who was the first to publish on the subject. In honor of Henry, the SI unit of inductance bears his name. One henry equals the inductance of a circuit with an induced voltage of one volt and an inducing current that changes one ampere per second.

Heinrich Hertz (1857-1894) – The discovery of radio waves, which was widely seen as confirmation of James Clerk Maxwell’s

electromagnetic theory and paved the way for numerous advances in communication technology, was made by German physicist Heinrich Hertz. In the late 1880s, Hertz carried out a comprehensive study of the waves to develop an understanding of their behavior. During the investigation he found that radio waves travel in straight lines and can be focused, diffracted, refracted and polarized.

Karl Jansky (1905-1950) – Karl Jansky, who discovered extraterrestrial radio waves while investigating possible sources of

interference in shortwave radio communications across the Atlantic for Bell Laboratories, is often known as the father of radio astronomy. Following his discovery, Jansky remained at Bell and there continued to contribute to improved radio communications, though he never had the opportunity to further investigate the radio waves that he had been the first to detect. The General Assembly of the International Astronomer's Union adopted the janskyas a unit of measurement for radio wave intensity as a tribute to him.

James Joule (1818-1889) – James Prescott Joule experimented with engines, electricity and heat throughout his life. Joule’s findings

resulted in his development of the mechanical theory of heat and Joule’s law, which quantitatively describes the rate at which heat energy is produced from electric energy by the resistance in a circuit. Initially many 19th century scientists were skeptical of Joule’s work, but his efforts proved fundamental to the modern understanding of thermodynamics.

William Thomson, Lord Kelvin (1824-1907) – William Thomson, known as Lord Kelvin, was one of the most eminent scientists of the

nineteenth century and is best known today for inventing the international system of absolute temperature that bears his name. He made

contributions to an array of different fields, including electricity, magnetism, thermodynamics, hydrodynamics, geophysics and telegraphy, publishing more than 650 papers during his lifetime. Thomson was also an extremely skilled engineer who patented around 70 inventions and was involved heavily in the laying of the first transatlantic telegraph cable.

Jack Kilby (1923-2005) – The integrated circuit fueled the rise of microelectronics in the latter half of the twentieth century and paved

the way for the Information Age. An American engineer, Jack Kilby, invented the integrated circuit in 1958, shortly after he began working at Texas Instruments. The magnitude of the invention’s importance is reflected in the fact that in 2000, Kilby shared the Nobel Prize in Physics, an award that has traditionally been bestowed for theoretical, rather than applied, work.

Klaus von Klitzing (1943-Present) – Klaus von Klitzing is a Nobel laureate who won the prestigious award in 1985 for his discovery of

the quantized Hall effect, sometimes referred to as the quantum Hall effect. Von Klitzing’s discovery resulted from his work exploring a phenomenon observed more than a century earlier by American physicist Edwin Hall. As Hall found, when a magnetic field is applied at a right angle to a thin layer of conducting or semiconducting material with an electrical current flowing through it, a transverse voltage (the Hall effect) develops across the material. By concentrating on two-dimensional systems maintained near absolute zero and exposed to extremely B magnetic fields, von Klitzing demonstrated that the Hall effect is not a continuous phenomenon, but rather occurs in discrete steps with a surprising amount of precision.

Paul Lauterbur (1929-2007) – Chemist Paul Lauterbur pioneered the use of nuclear magnetic resonance (NMR) for medical imaging.

He developed a technique, now known as magnetic resonance imaging (MRI), in the early 1970s that involves the introduction of gradients in the magnetic field employed for NMR and analysis of the data obtained to produce two-dimensional images of organs and soft tissues. The non-

invasive technique was later improved for practical application by Peter Mansfield, an English physicist. Lauterbur and Mansfield shared the Nobel Prize in Physiology or Medicine in 2003 for their work with MRI, now widely used.

Siegmund Loewe (1885-1962) – Siegmund Loewe was a German engineer and businessman that developed vacuum tube forerunners

of the modern integrated circuit. He pioneered both radio and television broadcasting, and the company he established with his brother, David Loewe, in 1923 was the foundation of today’s Loewe AG, a corporation that continues to be a leader in the consumer electronics industry.

Theodore Maiman (1927-Present) – Theodore Maiman built the world's first operable laser, which utilized a small synthetic rod with

silvered ends to produce a narrow beam of monochromatic light with a wavelength of approximately 694 nanometers. Ironically, Maiman’s first paper announcing this momentous achievement, which many other scientists had been racing to complete themselves, was rejected by Physical Review Letters. Since then, however, lasers have come to be widely employed for many purposes, including surgery, welding, special effects, barcode scanners, fiber optics, teeth whitening and reading CDs and DVDs.

James Clerk Maxwell (1831-1879) – James Clerk Maxwell was one of the most influential scientists of the nineteenth century. His

theoretical work on electromagnetism and light largely determined the direction that physics would take in the early twentieth century. Indeed, according to Albert Einstein, "One scientific epoch ended and another began with James Clerk Maxwell."

Walther Meissner (1882-1974) – Walther Meissner discovered while working with Robert Ochsenfeld that superconductors expel relatively

weak magnetic fields from their interior and are Bly diamagnetic. This

phenomenon, commonly known as theMeissner effect or the Meissner-Ochsenfeld effect, is related to the generation of screening currents along the surface of the superconductor that are able to cancel out the applied magnetic field. Following this discovery, Meissner was offered and accepted the technical physics chair at the Münich Institute of Technology in 1934.

Robert Millikan (1868-1953) – Robert Andrews Millikan was a prominent American physicist who made lasting contributions to both

pure science and science education. He is particularly well known for his highly accurate determination of the charge of an electron via his classic oil-drop experiment, a feat that along with his work on the photoelectric effect garnered him the Nobel Prize in Physics in 1923. Interestingly, Millikan’s investigational achievements promoted the general acceptance of both Niels Bohr's quantum theory of the atom and Albert Einstein’s photoelectric equation, an important step precipitating their recognition by the Nobel Foundation in 1922 and 1921, respectively, and, more importantly, placing modern physics on a firm foundation.

Karl Alexander Müller (1927-Present) – In their search for new superconductors, Swiss theoretical physicist Karl Alexander Müller

and his young colleague, J. Georg Bednorz, abandoned the metal alloys typically used in superconductivity research in favor of a class of oxides known as perovskites. The unusual direction of their work resulted in an important breakthrough in 1986 — superconductivity at a higher temperature than ever achieved before. When Müller and Bednorz announced their discovery, it caused such a stir in the scientific community that soon laboratories around the globe were experimenting with ceramic perovskites in hopes of attaining even higher superconducting temperatures.

Hans Christian Ørsted (1777-1851) – A discovery by Hans Christian Ørsted forever changed the way scientists think about electricity and

magnetism. While preparing to perform an experiment during a lecture at the University of Copenhagen, he found that the magnetized needle of a

compass was deflected whenever the electric current through a voltaic pile (an early form of the battery) was started or stopped. This surprising occurrence was solid evidence that electricity and magnetism are related phenomena.

Georg Ohm (1789-1854) – Georg Simon Ohm had humble roots and struggled financially throughout most of his life, but the German

physicist is well known today for his formulation of a law, termed Ohm’s law, describing the mathematical relationship between electrical current, resistance and voltage. Ohm’s law states that a steady current (I) flowing through a material of a given resistance is directly proportional to the applied voltage (V) and indirectly proportional to the resistance (R).

Heike Kamerlingh Onnes (1853-1926) – Heike Kamerlingh Onnes was a Dutch physicist who first observed the phenomenon

of superconductivity while carrying out pioneering work in the field of cryogenics. An important step on the way to this discovery was his success in producing liquid helium, a feat that enabled scientists to achieve colder experimental conditions than previously possible. Kamerlingh Onnes won the Nobel Prize in Physics in 1913 for his work with low temperatures that led to the liquefying of helium.

Wolfgang Pauli (1900-1958) – Austrian-born scientist Wolfgang Ernst Pauli made numerous important contributions to twentieth-

century theoretical physics, including explaining the Zeeman effect, first postulating the existence of the neutrino, and developing what has come to be known as the Pauli exclusion principle. A cornerstone of the modern understanding of matter, the exclusion principle garnered Pauli the Nobel Prize in Physics in 1945. According to the principle, no two electrons in an atom can share all four quantum numbers at the same time.

Edward Purcell (1912-1997) – Edward Mills Purcell was an American physicist who received half of the 1952 Nobel Prize for

Physics with for his development of a new method of ascertaining the magnetic properties of atomic nuclei. Known asnuclear magnetic resonance absorption, the method arose from the application of radar theory to the magnetic fields of atoms and was a significant advance over the magnetic resonance detection technique developed earlier by Isidor Rabi. Felix Bloch, with whom Purcell shared the Nobel Prize, independently made the same advance.

Isidor Isaac Rabi (1898-1988) – Isidor Isaac Rabi won the Nobel Prize in Physics in 1944 for his development of a technique for

measuring the magnetic characteristics of atomic nuclei. Rabi’s technique was based on the resonance principle first described by Irish physicist Joseph Larmor and it enabled more precise measurements of nuclear magnetic moments than had been previously possible. Rabi’s method was later independently improved upon by physicists Edward Purcell and Felix Bloch, whose work on nuclear magnetic resonance (NMR) garnered them the 1952 Nobel Prize in Physics and laid the foundations for magnetic resonance imaging (MRI).

Heinrich Rohrer (1933-Present) – Swiss physicist Heinrich Rohrer co-invented the scanning tunneling microscope (STM), a non-

optical instrument that allows the observation of individual atoms in three dimensions, with Gerd Binnig. The achievement garnered the pair half of the Nobel Prize in Physics in 1986. The Royal Swedish Academy of Sciences bestowed the other half of the prestigious award to Ernst Ruska for the invention of the electron microscope. The fact that the STM was a mere five years old when Binnig and Rohrer won the Nobel Prize (Ruska had invented his device back in the 1930s) is testament to the groundbreaking nature of the invention and the scientific community’s understanding of its tremendous import.

John Robert Schrieffer (1931-Present) – While still in graduate school, John Robert Schrieffer developed with John Bardeen and

Leon Cooper a theoretical explanation of superconductivity that garnered the trio the Nobel Prize in Physics in 1972. The BCS theory (the acronym

formed from the first letters of its creators’ surnames) applies specifically to low temperature superconductors. Schrieffer, however, has also been involved in research focusing on developing an equally successful theory of high temperature superconductivity.

Julian Schwinger (1918-1994) – Theoretical physicist Julian Schwinger used the mathematical process of renormalization to rid

the quantum field theory developed by Paul Dirac of serious incongruities with experimental observations that had nearly prompted the scientific community to abandon it. For this achievement, which firmly established quantum electrodynamics (QED) as an accurate predictor of the interactions of charged particles, Schwinger won the Nobel Prize in Physics in 1965. Physicists Richard Feynman and Sin-Itiro Tomonaga, who similarly refined QED theory at about the same time as Schwinger, shared the award with him that year.

Claude Shannon (1916-2001) – Claude Shannon was a mathematician and electrical engineer whose work underlies

modern information theory and helped instigate the digital revolution. He was the first person to recognize how Boolean algebra could be used to great advantage in the relay circuitry found in telephone routing switches, paving the way for its use in all digital circuitry and laying the groundwork for the modern computer and other electronic devices. Shannon also successfully applied mathematical theory to a number of other scientific disciplines, resulting in advances in game theory, artificial intelligence and theoretical genetics.

William Shockley (1910-1989) – William Bradford Shockley was head of the solid-state physics team at Bell Labs that developed the

first point-contact transistor, which he quickly followed up with the invention of the more advanced junction transistor. He shared the 1956 Nobel Prize in Physics with John Bardeen and Walter Brattain for his work on these projects. When Shockley left Bell Labs to establish his own company, he set up shop near Palo Alto, California. His research there

focused on developing silicon-based semiconductor devices, making him the first to introduce silicon into the area now known as Silicon Valley.

Werner von Siemens (1816-1892) – In 1866, the research of Werner von Siemens would lead to his discovery of the dynamo

electric principle that paved the way for the large-scale generation of electricity through mechanical means. He reported this discovery in a paper entitled “On the conversion of mechanical energy into electric current without the use of permanent magnets” to the Berlin Academy of Sciences in early 1867. Though scientists in other countries developed the self-exciting electric generator, or dynamo, at about the same time, von Siemens appears to be the first to truly realize its significance to society. The telegraph company he co-owned, Siemens & Halske, quickly began commercial production of dynamos, eventually followed by cables, electric lighting, telephones and other electrical devices. The company he founded is now the Siemens AG electronics conglomerate.

Nikola Tesla (1856-1943) – Awarded more than 100 patents over the course of his lifetime, Nikola Tesla was a man of considerable

genius and vision. He was reportedly born at exactly midnight during an electrical storm, an intriguing beginning for a man who would one day help light up all of America with the alternating current (AC) electric power systems he invented. In addition to his AC system, which allowed more efficient and safer power transmission over long distances than the direct current (DC) systems preferred by Thomas Edison, Tesla pioneered radio technology, experimented with X-rays, invented the first boat controlled remotely, and was a great proponent of wireless communication.

Joseph John Thomson (1856-1940) – Joseph John Thomson, better known as J. J. Thomson, was a British physicist who first

theorized and offered experimental evidence that the atom was a divisible entity rather than the basic unit of matter, as was widely believed at the time. A series of experiments with cathode rays he carried out near the end of the 19th century led to his discovery of the electron, a negatively charged atomic particle with very little mass. Thomson received the Nobel

Prize in Physics in 1906 for his work exploring the electrical conductivity of various gases.

Sin-Itiro Tomonaga (1906-1979) – Japanese theoretical physicist Sin-Itiro Tomonaga resolved key problems with the theory of

quantum electrodynamics (QED) developed by Paul Dirac in the late 1920s through the use of a mathematical technique he referred to as renormalization. Tomonaga’s work did not change the basic physical foundation of Dirac’s theory, which described the relationships between electrically charged particles and the electromagnetic field, but rather refined QED in order to make it consistent with the theory of special relativity and to show that the theory agrees quantitatively with results obtained experimentally to a great degree of accuracy. In 1965, Tomonaga received a portion of the Nobel Prize in Physics for his contributions to quantum electrodynamics.

Alessandro Volta (1745-1827) – Alessandro Volta was an Italian scientist whose skepticism of Luigi Galvani’s theory of animal

electricity led him to propose that an electrical current is generated by contact between different metals. Volta’s theoretical and experimental work in this area resulted in his construction of the first battery. Known as the voltaic pile, Volta’s battery made available for the first time a sustainable source of electrical current. Using the innovative apparatus, a number of his contemporaries, such as William Nicholson and Sir Humphry Davy, made important scientific advances in the early 19th century.

James Watt (1736-1819) – The Scottish instrument maker and inventor James Watt had a tremendous impact on the shape of

modern society. His improvements to the steam engine were a significant factor in the Industrial Revolution, and when the Watt engine was paired with Thomas Edison’s electrical generator in the late nineteenth century, the generation of electricity on a large scale was possible for the first time. Soon after, the streets of New York and other cities were illuminated with electric lamps.

Wilhelm Weber (1804-1891) – Researching magnetism with the great mathematician and astronomer Karl Friedrich Gauss in the

1830s, German physicist Wilhelm Weber developed and enhanced a variety of devices for sensitively detecting and measuring magnetic fields and electrical currents. Included among these devices was the electrodynamometer, which was capable of measuring electric current, voltage or power through the interaction of the magnetic fields of two coils. Utilizing this device, Weber experimentally validated André-Marie Ampère’s force law. Weber began developing a similar system of electric units around 1840 after Gauss developed a system of magnetic units expressed in terms of length, mass and time in the early 1830s.

Generators and Motors

Basic Magnetic Field

Magnets are pieces of metal that have the ability to attract other metals. Every magnet has two poles: a north and a south. Much like electrical charges, two similar magnetic poles repel each other; while opposite magnetic poles attract each other. Magnets have a continuous force around them that is known as a magnetic field. This field enables them to attract other metals. Figure 1 illustrates this force using bar and horseshoe magnets.

The shape of the magnet dictates the path the lines of force will take. Notice that the force in Figure 1 is made up of several lines traveling in a specific direction. It can be concluded that the lines travel from the magnet's north pole to its south. These lines of force are often called the magnetic flux. If the bar magnet is now bent to form a horseshoe magnet, the north and south pole are now across from each other. Notice in the horseshoe magnet how the lines of force are now straight, and that they travel from the north pole to the south. It will be revealed how generators and motors use these lines of force to generate electricity, as well as mechanical motion.

Magnetic Fields Around Conductors

When a current flows through a conductor, a magnetic field surrounds the conductor. As current flow increases, so does the number of lines of force in the magnetic field (Figure 2).

The right hand rule helps demonstrate the relationship between conductor current and the direction of force. Grasp a wire conductor in the right hand, put your thumb on the wire pointing upward, and wrap your four fingers around the wire. As long as the thumb is in the direction that current flows through the wire, the fingers curl around the wire in the direction of the magnetic field. Figure 3 demonstrates the right hand rule.

Polarity of Coils Cutting Through Lines of Force

A conductor can be twisted into a coil, which efficiently produces current when cutting the lines of force in a magnetic field. The more turns in this coil, the stronger the magnetic field. Furthermore, if the coil is wrapped around a piece of iron, the current becomes even stronger.

When needing to discover which poles are which in a conductor, it is important to notice which way the coils turn in order to apply the right hand rule. In addition, one should always look at which side of the coil is attached to the positive terminal of a power source such as a battery, and which side is attached to the negative. Figure 4 illustrates four different scenarios and the appropriate poles.

As a conductor cuts across the lines of force in a magnetic field, it generates a current. This method of inducing a current is called induction. There are three rules for induction:

1. When a conductor cuts through lines of force, it induces an electromotive force (EMF), or voltage.

2. Either the magnetic field or the conductor needs to be moving for this to happen.

3. If the direction of the cutting across the magnetic field changes, the direction of the induced EMF also changes.

Accordingly, Faraday's law states that induced voltage can be determined by the number of turns in a coil, and how fast the coil cuts through a magnetic field. Therefore, the more turns in a coil or the stronger the magnetic field, the more voltage induced.

In addition, current changes direction depending on which way it cuts across a magnetic field. As depicted in Figure 5, a coil cutting through a basic magnetic field in a clockwise direction will at first result in a current with positive polarity, but as it cuts across the same field in the opposite direction during the second half of its turn, the polarity becomes negative.

When current switches from positive to negative repeatedly, it is called alternating current, or A.C. Alternating current will be explained in more detail later.

DC Current

When a current is direct (D.C.) rather than alternating (A.C.), the polarity of that current never changes direction. Usually, when a coil turns in a clockwise direction, the first 180 degrees of the turn result in the induced current going in a positive direction. As mentioned above, however, the second 180 degrees result in the induced current going in a negative direction. In direct current, the current always travels in a positive direction. How is this possible? When inducing direct current, some mechanism must be employed to make sure the coils only cut through the magnetic field in one direction, or that the circuit only uses current from the coil cutting in that one direction. Devices such as D.C. generators employ a mechanism called a commutator to keep current flowing in one direction. Figure 6 shows direct current in the form of a sine wave. Notice that the current never has negative polarity, and is therefore always flowing in a positive direction.

Direct Current Generators

A generator is a device that turns rotary mechanical energy into electrical energy.

Simple D.C. generators contain several parts, including an armature (or rotor), a commutator, brushes, and field winding. A variety of sources can supply mechanical energy to the D.C. generator to turn its armature. The commutator changes the alternating current (A.C.) into direct current as it flows through the armature.

The stationary brushes, which are graphite connectors on the generator, form contact with opposite parts of the commutator. As the armature coil turns, it cuts across the magnetic field, and current is induced. At the first half turn of the armature coil

(clockwise direction), the contacts between commutator and brushes are reversed, or to put it another way, the first brush now contacts the opposite segment that it was touching during the first half turn while the second brush contacts the segment opposite the one it touched on the first half turn. By doing this, the brushes keep current going in one direction, and deliver it to and from its destination.

Direct Current Motors

Motors change electric energy into mechanical energy. Direct current motors and generators are constructed very similarly. They function almost oppositely at first because a generator creates voltage when conductors cut across the lines of force in a magnetic field, while motors result in torque-- a turning effort of mechanical rotation. Simple motors have a flat coil that carries current that rotates in a magnetic field. The motor acts as a generator since after starting, it produces an opposing current by rotating in a magnetic field, which in turn results in physical motion.

This is accomplished as a conductor is passed through a magnetic field, then the opposing fields repel each other to cause physical motion. The left hand rule can be used to explain the way

a simple motor works (Figure 9). The pointer finger points in the direction of the magnetic field, the middle finger points in the direction of the current, and the thumb shows which way the conductor will be forced to move.

A self-excited motor produces its own field excitation. A shunt motor has its field in parallel with the armature circuit, and a series motor is when the field is in a series with the armature.

When the conductor is bent into a coil, the physical motion performs an up and down cycle. The more bends in a coil, the less pulsating the movement will be. This physical movement is called torque, and can be measured in the equation:

T = kt  ia

T = torque

kt = constant depending on physical dimension of motor

 = total number of lines of flux entering the armature from one N pole

ia = armature current

Alternating Current

Much like the process of producing direct current, the process of producing an alternating current requires a conductor loop spinning in a magnetic field. As a matter of fact, the process is the same for both types of current, except that the alternating current is never changed into direct current through the use of a commutator. The conductor loop, or coil, cuts through lines of force in a magnetic field to induce A.C. voltage at its terminals. Each complete turn of the loop is called a "cycle." The alternating current wave is pictured in Figure 10.

Notice what segment of the wave consists of one cycle, and which is the part of the wave from point A to the next point A. If we divide the wave into four equal parts, the divisions happen at points A, B, C, and D. We can read the turn of the coil and how it relates to the wave produced. From A to B is the first quarter turn of the coil, from B to C is the second quarter turn, from C to D is the third quarter turn, and from D to A is the final quarter turn.

It is important to note that degree markings on a horizontal axis refer to electrical degrees and are not geometric. The example above is for a single pole generator. However, if this were a double pole generator, then 1 cycle would happen at each 180 degrees rather than 360 degrees, and so on.

Alternating Current Generator

An alternating current generator, or alternator, produces an alternating current, which means the polarity of the current changes direction repeatedly. This type of generator requires a

coil to cut across a magnetic field, and is attached to two slip rings connected to brushes. The brushes deliver the current to and from the load destination, thus completing the circuit.

During the first half turn, the coil cuts across the field near the magnet's north pole. Electrons go up the wire, and the lower slip ring becomes positively charged. When the coil cuts near the south pole of the wire during the second half turn, the lower slip ring becomes negatively charged, and electrons move down the wire. The faster the coil turns, the faster the electrons move, or to put it another way, the more frequency is increased, or the more hertz per second, the stronger the current.

Alternating Current Motor

An alternating current motor is similar to the direct current motor except for a few characteristics. Instead of the rotor field reversing every half turn, the stator field reverses every half turn.

There are several different types of alternating current motors. The most common type is the polyphase induction motor, which contain a stator and a rotor, where the stator is attached to the A.C. supply. When the stator winding becomes energized, a rotating magnetic field is created. An EMF is induced as the field goes across the inductors and current flows through them. Torque is therefore exerted on the rotor conductors carrying current in the stator.