Electricity

• 1. Introduction

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  Electricity is the set of physical phenomena tied to matter that carries an electric charge. Long before anyone could name it, people felt it. Ancient Egyptian texts from 2750 BCE described electric fish as the protectors of all other fish. Patients with gout or headache were told to touch these fish, in the hope that a powerful jolt might cure them. For most of human history, this force stayed an intellectual curiosity, little more than a parlor trick with amber and cat's fur. So how did a numbing shock from a catfish become the foundation of modern industrial society? What did it take to move from feathers clinging to a rubbed rod to billions of transistors packed into a few centimetres square? And why did one scientist tell a politician it might one day be taxed? The answers run through electric fields, magnets, kites flown in storms, and a battery built from zinc and copper.

• 2. Amber And First Sparks

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  Around 600 BCE, Thales of Miletus rubbed amber and watched it pull light objects toward it. He believed friction made the amber magnetic, unlike minerals such as magnetite that needed no rubbing. He was wrong about the magnetic cause, but later science would prove a real link between magnetism and electricity. In 1600, the English scientist William Gilbert wrote De Magnete, carefully separating the lodestone effect from static electricity produced by rubbing amber. He coined the Neo-Latin word electricus, meaning of amber or like amber, from elektron, the Greek word for amber. From that root came the English words electric and electricity, first appearing in print in Thomas Browne's Pseudodoxia Epidemica of 1646. Isaac Newton later made early investigations, and an idea written in his book Opticks is arguably the beginning of the field theory of the electric force. Otto von Guericke, Robert Boyle, Stephen Gray and C. F. du Fay carried the work forward in the 17th and early 18th centuries, setting the stage for a man who would sell his possessions to fund his experiments.

• 3. Kites And Frog Legs

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  In June 1752, Benjamin Franklin is reputed to have attached a metal key to the bottom of a dampened kite string and flown it into a storm-threatened sky. Sparks jumping from the key to the back of his hand showed that lightning was electrical in nature. Franklin also explained the Leyden jar, a device for storing large amounts of charge, by proposing that electricity consisted of both positive and negative charges. In 1775, Hugh Williamson reported experiments to the Royal Society on the shocks of the electric eel, and the surgeon John Hunter described the structure of the fish's electric organs that same year. In 1791, Luigi Galvani published his discovery of bioelectromagnetics, showing that electricity carried signals from neurons to muscles. Galvani's earlier work twitched the legs of dead frogs with animal electricity, and that image lingered. Mary Shelley knew of such resuscitation reports when she wrote Frankenstein in 1819, though she never names how the monster is revived. The revitalization of monsters with electricity became a stock theme in later horror films.

• 4. Charge And Coulomb

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  A proton carries a charge of exactly 1.602176634, the value defined as the elementary charge. No object can hold a charge smaller than this, and any charge is a multiple of it. By modern convention, electrons are negative and protons positive, but before these particles were known, Benjamin Franklin defined positive charge as what a glass rod gains when rubbed with silk. Charles-Augustin de Coulomb investigated charge in the late eighteenth century and deduced that it comes in two opposing forms. A lightweight ball charged by a glass rod repels a second ball charged the same way, yet attracts a ball charged by an amber rod. From this came the axiom that like-charged objects repel and opposite-charged objects attract. Coulomb's law gives the magnitude of the force, relating it to the product of the charges with an inverse-square dependence on distance. The electromagnetic force is second only to the strong interaction in strength. The force pushing two electrons apart is 1042 times the gravitational attraction pulling them together. Charge is also a conserved quantity, so the net charge in an electrically isolated system stays constant no matter what happens inside it.

• 5. Current Fields And Motors

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  The movement of electric charge is an electric current, measured in amperes. Current can flow through electrical conductors but not through an insulator, and the particles themselves may drift only fractions of a millimetre per second. The driving electric field, by contrast, propagates at close to the speed of light, letting signals race along wires. In 1820, while preparing a lecture, Hans Christian Orsted saw a current in a wire disturb a magnetic compass needle. He had discovered electromagnetism, and noted that the electric conflict acts in a revolving manner. Ampere then found that two parallel wires attract when their currents flow the same way and repel when they flow opposite. This relationship led Michael Faraday to invent the electric motor in 1821. His homopolar motor used a permanent magnet in a pool of mercury, with a current-carrying wire dipped in, circling the magnet as long as the current flowed. In 1831, Faraday found that a wire moving perpendicular to a magnetic field developed a potential difference across its ends. That insight, electromagnetic induction, let him build the first electrical generator the same year, turning the motion of a rotating copper disc into electrical energy.

• 6. Volts Resistors And Storage

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  Electric potential is the energy needed to bring a unit test charge from infinite distance to a point, usually measured in volts. One volt is the potential for which one joule of work moves one coulomb from infinity. Earth itself is the common reference, assumed to be at the same potential everywhere and electrically uncharged. The resistor is the simplest passive element, resisting current and dissipating energy as heat. Georg Ohm mathematically analysed the circuit in 1827, and the ohm honours him with the symbol of the Greek letter omega. The capacitor descends from the Leyden jar, storing charge between two conducting plates separated by a thin insulating dielectric. Its unit, the farad, is named after Michael Faraday. The inductor stores energy in a magnetic field, freely allowing steady current but opposing rapid change, and its unit, the henry, honours Joseph Henry, a contemporary of Faraday. Storing electricity itself remains difficult, so supply must usually match demand. Variable wind and solar power make that match harder, and storage technologies are stepping in, including batteries, chemical storage such as hydrogen, thermal storage, and mechanical methods such as pumped hydropower.

• 7. From Curiosity To Industry

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  By the late 19th century, electrical engineering saw its greatest progress, carried by figures such as Alexander Graham Bell, Thomas Edison, Nikola Tesla and George Westinghouse. In 1864, James Clerk Maxwell analysed electromagnetic waves theoretically, developing equations that unified electric field, magnetic field, charge and current. He proved that such a wave travels through a vacuum at the speed of light, making light itself a form of electromagnetic radiation. In 1887, Heinrich Hertz found that electrodes lit by ultraviolet light produce sparks more easily. In 1905, Albert Einstein explained the photoelectric effect as light energy carried in discrete quantized packets, work that led to the quantum revolution and won him the Nobel Prize in Physics in 1921. The first working transistor, a germanium point-contact device, was invented by John Bardeen and Walter Houser Brattain at Bell Labs in 1947, followed by the bipolar junction transistor in 1948. A modern integrated circuit may now contain many billions of miniaturised transistors in a region only a few centimetres square. The steam turbine that Sir Charles Parsons invented in 1884 still spins the generators that supply this power today.

• 8. Living Current And Lore

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  A current as low as a microamp can be detected as an electrovibration effect, while the perception threshold for mains-frequency electricity sits around 0.1 mA to 1 mA. Push the current higher and it causes muscle contraction, fibrillation of the heart, and tissue burns. Because a live conductor shows no visible sign, electricity is a particular hazard, and electrocution is still used for judicial execution in some US states, though rare by the end of the 20th century. Nature wields the same force. Certain crystals such as quartz, and even sugar, generate a potential difference when pressed, an effect called piezoelectricity that Pierre and Jacques Curie discovered in 1880. Sharks detect changes in electric fields through electroreception, and the electric eel, of the order Gymnotiformes, stuns prey using modified muscle cells called electrocytes. The cultural grip is just as old. In the 1850s, British politician William Ewart Gladstone asked Faraday why electricity was valuable, and Faraday is said to have answered, One day sir, you may tax it. Snopes.com calls the anecdote apocryphal, since it appears in no account by Faraday or his contemporaries and surfaced only well after his death. Today the force fades from notice until it stops, and the people who keep it flowing, like the lineman in Jimmy Webb's 1968 song Wichita Lineman, are still cast as heroic, wizard-like figures.