Electricity

Electricity is a set of phenomena linked to the presence and motion of matter that has an electric charge. Electricity is related to magnetism. Both are part of electromagnetism, as described by Maxwell's equations. Many common events are connected to electricity, including lightning, static electricity, electric heating, electric discharges and many others.

A positive or negative electric charge creates an electric field. The motion of electric charge carriers is an electric current, and it produces a magnetic field. In most uses, Coulomb's law describes the force acting on an electrically charged particle. Electric potential is the work needed to move an electric charge from one place to another within an electric field. It is usually measured in volts.

Electricity plays a central role in many modern technologies. It is used in electric power, where electric current gives energy to equipment. It is also used in electronics, which deals with electrical circuits containing active components such as vacuum tubes, transistors, diodes and integrated circuits, along with related connection technologies.

People have studied electrical effects since ancient times, but understanding grew slowly until the 1600s and 1700s. The theory of electromagnetism developed in the 1800s and was a major step forward. By the end of that century, electrical engineers had brought electricity into factories and homes. This fast growth in electrical technology helped drive the Second Industrial Revolution, and electricity changed both industry and society.

Today, electricity is used in transport, heating/cooling, lighting, communications, and computation. This makes it the foundation of modern industrial society.

Main articles: History of electromagnetic theory and History of electrical engineering

See also: Etymology of electricity

Long before people understood electricity, they knew about shocks from electric fish. Ancient Egyptian writings from about 2750 BCE called them the "protectors" of other fish. Later, ancient Greek, Roman and Arab naturalists and physicians also wrote about them. Pliny the Elder and Scribonius Largus described the numbing feeling from electric shocks given by electric catfish and electric rays. They knew such shocks could travel along conducting objects. Patients with gout or headache were told to touch electric fish, hoping the jolt might cure them. Ancient peoples around the Mediterranean knew that rods of amber rubbed with cat's fur could attract light objects. Around 600 BCE, Thales of Miletus studied static electricity. He believed rubbing made amber magnetic, unlike magnetite, which needed no rubbing. He was wrong about the cause, but later science proved a link between magnetism and electricity.

For a very long time, electricity was mostly an interesting question for thinkers, until 1600, when the English scientist William Gilbert wrote De Magnete. He carefully studied electricity and magnetism, separating the lodestone effect from static electricity made by rubbing amber. He created the Neo-Latin word electricus, from the Greek word for amber. The English words "electric" and "electricity" first appeared in print in Thomas Browne's Pseudodoxia Epidemica in 1646. Isaac Newton made early investigations, and an idea he wrote in Opticks is arguably the start of the field theory of the electric force. Further work was done by Otto von Guericke, Robert Boyle, Stephen Gray and C. F. du Fay. In the 1700s, Benjamin Franklin researched electricity widely, even selling his possessions to pay for his work. In June 1752 he attached a metal key to a damp kite string and flew the kite in a stormy sky. Sparks jumping from the key to his hand showed that lightning was electrical. He also explained how the Leyden jar stored large amounts of electrical charge. In 1775, Hugh Williamson reported experiments on the shocks of the electric eel. John Hunter described the structure of its electric organs (the surgeon and anatomist was John Hunter). In 1791, Luigi Galvani published his discovery of bioelectromagnetics, showing that electricity was how neurons passed signals to the muscles. Alessandro Volta's voltaic pile of 1800, made of alternating zinc and copper layers, gave scientists a more reliable source of electrical energy than electrostatic machines. The unity of electromagnetism was recognised by Hans Christian Ørsted and André-Marie Ampère in 1819–1820. Michael Faraday invented the electric motor in 1821, and Georg Ohm analysed the electrical circuit in 1827. James Clerk Maxwell clearly linked electricity, magnetism and light in "On Physical Lines of Force" in 1861 and 1862. The late 1800s saw the greatest progress in electrical engineering, through people such as Alexander Graham Bell, Ottó Bláthy, Thomas Edison, Galileo Ferraris, Oliver Heaviside, Ányos Jedlik, William Thomson, 1st Baron Kelvin, Charles Algernon Parsons, Werner von Siemens, Joseph Swan, Reginald Fessenden, Nikola Tesla and George Westinghouse. Electricity changed from a scientific curiosity into an essential tool for modern life. In 1887, Heinrich Hertz found that electrodes lit by ultraviolet light make electric sparks more easily. In 1905, Albert Einstein published a paper explaining the photoelectric effect as light energy carried in small quantum packets, which give energy to electrons and led to the quantum revolution. Einstein won the Nobel Prize in Physics in 1921 for "his discovery of the law of the photoelectric effect". The photoelectric effect is also used in photocells, such as those found in solar panels. The first solid-state device was the "cat's-whisker detector", used in radio receivers in the 1900s. A thin wire touched a germanium crystal to detect a radio signal. In solid-state parts, current flows through solid materials designed to switch and boost it, carried by negatively charged electrons and positively charged holes. This is understood through quantum physics and usually happens in a crystalline semiconductor. Solid-state electronics grew with transistor technology. The first working transistor, a germanium-based point-contact transistor, was invented by John Bardeen and Walter Houser Brattain at Bell Labs in 1947. The bipolar junction transistor followed in 1948.

Concepts

Electric charge is carried by tiny particles such as electrons and protons. Electrons are said to have a negative charge, and protons have a positive charge. Like charges push each other away, and opposite charges pull toward each other. Charge can be measured and can move through a material as an electric current, which is measured in amperes. Current flows through electrical conductors but not through insulators. The electric field, introduced by Michael Faraday, surrounds charged objects and pushes on other charges. Electric potential is linked to this field. The difference in electric potential between two points is called voltage.

In 1820, Hans Christian Ørsted found that electricity and magnetism are connected. This is part of electromagnetism. This connection led to the invention of the electric motor. An electric circuit is a closed path that lets charge flow to do a useful job. Circuits can use parts such as resistors and capacitors. Electric power measures how fast energy is moved by a circuit. Electronics uses parts such as transistors and semiconductors to control the flow of electrons. In 1864, James Clerk Maxwell showed that changing electric and magnetic fields create electromagnetic waves, and that light is one form of these waves.

Production, storage and uses

See also: Electric power transmission and Mains electricity

In the 6th century BC, the Greek philosopher Thales of Miletus rubbed amber rods to study how to make electricity. This method, now called the triboelectric effect, can lift light objects and make small sparks, but it does not make much electricity. A useful source of electricity came later, with the voltaic pile in the eighteenth century. Its modern version, the electrical battery, stores energy in chemicals and releases it when needed. Today, most electrical power is made by generators. These can be turned by steam from burning fossil fuel, by heat from nuclear reactions, or directly by the kinetic energy of wind or moving water. The steam turbine, invented by Sir Charles Parsons in 1884, is still used to turn steam into motion for generators. Solar panels work differently. They turn solar radiation directly into electricity using the photovoltaic effect. Because of concerns about the environment and climate change, people are focusing more on renewable sources. Wind and solar power now cost less, which helps the world move away from fossil fuels in an energy transition.

In the late nineteenth century, the transformer was invented. It let electrical power travel at a higher voltage and lower current, which made it more efficient. This allowed electrical transmission to carry electricity from large power stations over long distances. Those power stations benefit from economies of scale. Electricity is hard to store, so supply must usually match demand, and some reserve is kept to protect the grid. As more variable renewable energy joins the grid, storage becomes more important. There are several storage methods, and each is at a different level of technology readiness. These include batteries, chemical storage such as hydrogen, and storage using heat or movement, such as pumped hydropower.

Electricity is a very convenient way to move energy, and it has many uses. The practical incandescent light bulb, invented in the 1870s, made lighting one of the first public uses of electrical power. It replaced open gas flames, which were dangerous. The Joule heating effect used in filament bulbs is also used for electric heating. Electricity can also power refrigeration, air conditioning and heat pumps. Electrification is expected to help with decarbonisation, including electric vehicles for transport and heat pumps for heating. The electric motor provides clean and efficient power. It is used in machines that stay in one place, like a winch, and in vehicles that carry a battery or get power through a pantograph. Electric buses, trains and electric cars are used today. Electricity is also used in telecommunications and electrical telegraphs. With the transcontinental and transatlantic telegraph systems of the 1860s, messages could travel around the world in minutes.

Electricity and the natural world

Main article: Electrical injury

Electricity can travel through a person's body when a voltage is applied. The higher the voltage, the more current flows. People can feel even a small current from mains electricity. A strong enough current can make muscles tighten, disturb the heartbeat through fibrillation, and cause tissue burns. Electricity can be hidden, since a live wire may show no sign of danger, so it is especially risky. Electric shocks can be very painful, and electricity has sometimes been used to hurt people through torture. Death from an electric shock, called electrocution, has been used as a judicial execution in some US states, though this had become very rare by the end of the 20th century.

Main article: Electrical phenomena

Electricity is not a human invention. It occurs in nature, most notably in lightning. Many everyday actions, such as touch, friction, and chemical bonding, happen because of electric fields between tiny atoms. The Earth's magnetic field comes from a natural dynamo, which is made of currents moving inside the planet's core. Some crystals, such as quartz and even sugar, create a voltage across their faces when pressed. This is called piezoelectricity, from the Greek word piezein, meaning "to press." It was discovered in 1880 by Pierre and Jacques Curie. Some animals, such as sharks, can sense changes in electric fields, an ability called electroreception. Others, called electrogenic animals, create their own voltages to hunt or defend themselves, such as the electric fish of several groups. The Gymnotiformes order, including the well-known electric eel, uses high voltages from special muscle cells called electrocytes. All animals send messages along their cell membranes using voltage pulses called action potentials, which let neurons and muscles communicate. Action potentials also help some plants coordinate their activities.

Cultural perception

It is said that in the 1850s, British politician William Ewart Gladstone asked the scientist Michael Faraday why electricity was valuable. Faraday supposedly replied, "One day sir, you may tax it." However, this story is not trusted, because it does not appear in any writings by Faraday or from his time. In the 1800s and early 1900s, electricity was still new to many people, even in the Western world. Popular culture of the time often showed it as a mysterious, almost magical force that could bring the dead back to life. This idea began with the 1771 experiments of Luigi Galvani. He showed that the legs of dead frogs twitched when touched by animal electricity. Mary Shelley knew about these results when she wrote Frankenstein in 1819. Later, bringing monsters back to life with electricity became a common idea in horror films.

As electricity became central to the Second Industrial Revolution, people who worked with it were more often shown in a positive light. One example is Rudyard Kipling's 1907 poem Sons of Martha. Electric vehicles appeared in adventure stories by Jules Verne and in the Tom Swift books. Famous electrical inventors, such as Thomas Edison, Charles Steinmetz, and Nikola Tesla, were often seen as having wizard-like powers. Later, when electricity became a part of everyday life, popular culture mostly noticed it when it stopped flowing, which usually meant trouble. Workers who keep it flowing are still often shown as heroes. One example is the hero of Jimmy Webb's song "Wichita Lineman" (1968).