Electricity

Electricity is also associated with many biological processes. In the human body, electrical signals travel along nerves, carrying information to and from the brain. Electrical signals tell the brain what the eyes see, what the ears hear, and what the fingers feel. Electrical signals from the brain tell muscles to move. Electrical signals even tell the heart when to beat.

One of the most important properties of electricity is electric energy. During the 1800's, people learned to harness electricity to do work. This new source of energy had so many practical applications that it greatly changed the way people lived. Inventors and scientists learned how to generate electric energy in large quantities. They found ways to use that energy to produce light, heat, and motion. They developed electric devices that enabled people to communicate across great distances and to process information quickly. The demand for electric energy grew steadily during the 1900's. Today, most people cannot imagine life without electric energy.

In homes. Electric appliances, such as dishwashers, toasters, vacuum cleaners, and washing machines, save hours of labor. Electric ranges, microwave ovens, and food processors help us prepare meals quickly and easily. Refrigerators and freezers preserve food. Air conditioners and electric fans cool our homes, while electric heaters provide warmth and hot water. Television, radio, video games, compact disc players, and videocassette recorders furnish entertainment. Electric lights let us make use of the nighttime hours.

In industry. Modern industry would be impossible without electric energy. Factories produce many products on assembly lines using electrically operated conveyor belts and equipment. Manufacturers use electric instruments to ensure correct product sizes and quality. Drills, saws, and many other small tools run on electric energy. Electric motors run elevators, cranes, and most other large machinery.

In communication. Electric energy powers almost every device people use to communicate. Telephones, TV's, radios, fax machines, and computer modems all run on electric energy. Communications satellites use electric energy from devices called solar cells to relay information around the world. TV and radio signals are partly electrical, as are telephone, computer, and fax signals that travel along wires or thin strands of glass called optical fibers.

In transportation. Electric energy supplies power to subways, trolleys, and trains that carry millions of people to and from work. Most cars use electric sparks to ignite the gasoline that powers the engine. Electric devices help reduce fuel consumption and air pollution in gasoline engines. Many controls in airplanes and ships are electrically powered.

In medicine and science. Health care workers use numerous electric instruments to examine patients and perform medical tests. For example, X-ray machines and magnetic resonance imagers enable doctors to see inside our bodies. Electrocardiograph machines record tiny electrical signals from the heart, helping doctors to diagnose heart disease.

Scientists from every field use electric devices to conduct research. Microbiologists, for example, use powerful instruments called scanning electron microscopes to learn the secrets of living cells. Physicists use electrically operated particle accelerators to probe the interiors of atoms. Huge telescopes with electric motors help astronomers study planets, stars, and galaxies.

Opposite charges, also called unlike charges--negative and positive--attract one another. Like charges--positive and positive, or negative and negative--repel (push away) one another. The power to attract and repel other charges is caused by invisible influences called electric fields that surround each charged particle. Because of the fields, particles attract or repel one another even when they are not touching.

Atoms. Quarks combine to form protons and neutrons. Protons and neutrons, in turn, combine with electrons to make up atoms. In an atom, protons and neutrons join to form a tiny core, called the nucleus.

The positively charged nucleus of an atom attracts negatively charged electrons. The nucleus has a positive charge because it contains protons but no electrons. The negative electrons whirl around the positive nucleus in somewhat the same way planets orbit the sun.

Each type of atom has a different number of protons in its nucleus. For example, hydrogen, the simplest atom, has only 1 proton in its nucleus. An oxygen atom has 8 protons. Iron has 26. Uranium has 92. Normally, an atom has an equal number of protons and electrons. As a result, the negative charges of the electrons exactly balance the positive charges of the protons. The atom is, therefore, electrically neutral.

Ions. Sometimes an atom loses or gains one or more electrons. If it gains an electron, the atom takes on a negative charge. If it loses an electron, the atom takes on a positive charge. Atoms that carry an electric charge are called ions. Most ions are positive, and the word ion used alone usually means an atom that has lost one or more electrons. Positive and negative ions attract one another and can combine to form solid materials. Ordinary table salt, for example, consists of sodium and chlorine. Each sodium atom gives up one electron to form a positive sodium ion. The chlorine takes on this electron to become a negative chloride ion. The strong electrical attraction between the ions makes salt a solid material with a high melting point.

An atom becomes an ion when it gains or loses an electron and so acquires an electric charge. A normal atom, left, has an equal number of positive protons and negative electrons. If it loses an electron, right, it becomes a positively charged ion. From The World Book™ Multimedia Encyclopedia ©1998 World Book, Inc., 525 W. Monroe, Chicago, IL 60661. All rights reserved. World Book diagram by Tom Brucker, Precision Graphics.

Molecules. Neutral atoms often share electrons with other atoms. Atoms that share electrons become electrically attracted to one another. The attraction causes the atoms to join and form molecules. For example, two hydrogen atoms can share electrons with one oxygen atom to make a water molecule. The electrons tend to spend more time near the oxygen atom, giving it a slightly negative charge. The two hydrogen atoms take on slightly positive charges. The electric attraction between these charged atoms holds the water molecule together.

Static electricity. Sometimes, a large number of atoms in an object gain or lose electrons. When such a gain or loss happens, the entire object takes on an electric charge. The term static electricity describes situations where objects carry electric charge.

Static electricity occurs, for example, when you rub a balloon on your shirt. The friction between the cloth and the balloon causes electrons to transfer from your shirt to the balloon. The shirt then has an overall positive charge because it has more protons than electrons. The balloon takes on a negative charge because it has extra electrons. The balloon will then stick to the shirt or to another surface, such as a wall.

Similarly, when you walk across a rug on a dry day, friction between your shoes and the rug transfers electrons from your body to the rug, giving your body a positive charge. If you touch a doorknob or other metal object, electrons may jump from the object to your body. You may see a spark and feel a slight shock.

Lightning results from static electricity. Scientists believe that raindrops tossed in the winds of thunderclouds build up electric charge. Parts of the cloud become positively charged, while other parts become negatively charged. Charge may jump between different parts of the cloud, or from the cloud to the ground. The result is the huge electric spark we call lightning.

Static electricity has many uses in homes, businesses, and industries. For example, the copying machines found in most offices are electrostatic copiers. They make duplicates of printed or written material by attracting negatively charged particles of toner (powdered ink) to positively charged paper. Static electricity is also used in air cleaners called electrostatic precipitators. These devices put a positive electric charge on particles of dust, smoke, bacteria, or pollen in the air. Negatively charged collector plates attract the positive particles out of the air.

Conductors. Materials that conduct electricity contain charged particles that are free to move throughout the material. If extra electric charge is applied to a conductor, the charged particles will not stay in place but will spread over the material's surface. In most conductors, the free particles are electrons that are not attached to atoms. In some conductors, the free particles are ions.

Metals are good conductors because they contain a large number of free electrons. Most wires used to carry electric energy are made of metal, usually copper. Some liquids are also conductors. Salt water, for example, is a conductor because it contains sodium and chloride ions that are free to move about.

Some gases are also conductors. If a gas is extremely hot, its atoms move so fast that they collide hard enough to tear electrons free. Then the gas becomes a type of electric conductor called plasma. The hot, glowing gas inside a fluorescent light is one example of plasma. The hot gases that make up the sun and other stars are also plasma.

In most conductors, moving electrons continuously collide with atoms and lose energy. But in some materials, called superconductors, electrons move perfectly freely without losing energy. Superconductors only work at very cold temperatures. Because they require extreme cold, superconductors are only used in special situations. Someday, however, superconductors may be used to make highly efficient motors, generators, and power lines.

Insulators. In materials called insulators, electrons are tightly bound to atoms and are not free to move around. If extra electric charge is applied to an insulator, the charge will stay in place and will not move through the material. Glass, rubber, plastic, dry wood, and ordinary dry air are good insulators.

Insulators are important for electrical safety. Most electrical cords are made from a conducting material covered with an insulating material, such as rubber or plastic. The insulator makes the cords safe to touch, even when they are plugged into an outlet.

Semiconductors. Some materials conduct electric charge better than insulators but not as well as conductors. These materials are called semiconductors. Silicon is the most commonly used semiconductor. By adding small amounts of other substances to a semiconductor, engineers can adjust its capacity to conduct electric charge. Semiconductors are essential to the operation of computers, calculators, radios, television sets, video games, and many other devices.

Resistance refers to a material's opposition to the passage of electric charges through it. Resistance occurs when electrons moving in the material collide with atoms and give up energy. The energy the electrons give up is converted into heat. A good conductor, such as copper, has low resistance. The semiconductor silicon has higher resistance. Insulators, such as glass or wood, have such high resistance that it is nearly impossible for electric charges to flow through them. Superconductors offer no resistance to the flow of electric charges.

Resistance depends not only on the type of material but also on its size and shape. For example, a thin copper wire has more resistance than a thick one. A long wire has greater resistance than a short one. A material's resistance may also vary with temperature.

Direct and alternating current. Current that flows steadily in one direction is called direct current (DC). A battery produces direct current. Sometimes current flows back and forth, changing direction rapidly. It is then called alternating current (AC). The current in household wiring is alternating current. In the United States and Canada, household current reverses direction 120 times per second, completing 60 full cycles.

Sources of current. By itself, a conductor does not have electric current flowing in it. But if a positive charge is applied to one end of the conductor, and a negative charge to the other end, then electric charge will flow through the conductor. Because positive and negative charges attract, some type of energy must be supplied to separate the charges and keep them at opposite ends of the conductor. The energy may come from chemical action, motion, sunlight, or heat.

Batteries produce electric energy by means of chemical action. A battery has two structures called electrodes, each made from a different chemically active material. Between the electrodes, the battery contains a liquid or paste called an electrolyte, which conducts electric current. The electrolyte helps promote chemical reactions at each electrode. As a result of the chemical reactions, a positive charge builds up at one electrode and a negative charge builds up at the other. Electric current will then flow from the positive electrode, through a conductor, to the negative electrode.

In a flashlight battery, the flat end is the negative electrode. The end with a bump connects to the positive electrode. When a wire links the electrodes, a current flows. The electric energy is converted to light if it passes through a flashlight bulb. Chemical reactions in the electrolyte keep the electrodes oppositely charged and so keep the current flowing.

Eventually, the chemical energy runs out and the battery can no longer produce electric energy. Some worn-out batteries must be discarded. Others, called rechargeable batteries, can be charged again by passing electric current through them.

Generators change mechanical energy into electric energy. In a generator, a source of mechanical energy spins coils of wire near a magnet to produce electric current. A generator works because moving a conductor near a magnet produces a current in the conductor. Most generators produce alternating current.

Generators furnish most of the electric energy people use. In a car, a small generator called an alternator is turned by the engine and produces electric energy that recharges the car's battery. A large generator in an electric power plant can provide enough electric energy for a city of 2 million people. Electric current from the generator reaches homes, factories, and offices through vast networks of power lines.

Solar cells, also called photovoltaic cells, convert sunlight into electric energy. Solar cells power most artificial satellites and other spacecraft as well as many handheld calculators. Photovoltaic cells are made from semiconducting materials, usually specially treated silicon. Energy from the sun forces negative and positive charges in the semiconductor to separate. The charges will then flow through a conductor.

Piezoelectric crystals are nonmetallic minerals that develop electric charge along their surfaces when stretched or compressed. Quartz is the most common piezoelectric crystal. Some microphones use piezoelectric crystals to convert sound energy into electric energy for recording or radio broadcasting. Modern gas ranges have piezoelectric crystals instead of pilot lights. The crystals produce electric sparks that ignite the gas.

An electric circuit is a path that electric current can follow between a device, such as a light bulb, and an energy source, such as a battery. With the switch open, a gap separates the connecting wires so that the current cannot complete its path. From The World Book™ Multimedia Encyclopedia ©1998 World Book, Inc., 525 W. Monroe, Chicago, IL 60661. All rights reserved. World Book diagram by Tom Brucker, Precision Graphics.

A simple circuit. Suppose you want to make a battery-powered light bulb shine. Electric current will only flow if there is a complete circuit that leads from the battery to the bulb and back to the battery. To make the circuit, connect a wire from the positive terminal of the battery to the light bulb. Then, connect another wire from the bulb back to the negative terminal. Electric current will then flow from the battery's positive terminal, through the light bulb, to the battery's negative terminal.

Inside the bulb is a thin wire called a filament. The filament is made from a material with greater resistance than the wires linking the battery and bulb. The moving electrons that make up the current collide with atoms in the filament and give up most of their energy. The released energy heats the filament, which glows and gives off light.

Series and parallel circuits. A single battery or generator often powers more than one electric device. In such cases, circuit designs called series circuits and parallel circuits are necessary.

A series circuit has only one path. The same current flows through all parts of the path and all electric devices connected to it. Flashlights, some Christmas tree lights, and other simple devices use series circuits. In a parallel circuit, the current splits to flow through two or more paths. Parallel circuits enable a single energy source to provide current to more electric devices than a series circuit could. Household lights and appliances are connected in parallel circuits.

Many circuits include some parts that are series and some that are parallel. An extremely complex circuit, like that in a computer or TV, has millions of parts connected in various series and parallel combinations.

Electric and magnetic fields. When most people think of an electric current, they think of moving electrons carrying charges through a wire. Actually, most of the energy flows in electric and magnetic fields surrounding the wire. Energy from the fields enters the wires and replaces energy the electrons lose through resistance. The battery, generator, or other energy source continually restores energy lost from the fields.

In DC circuits, electrons flow from one battery terminal, through the circuit, to the other terminal. But the energy of the electric and magnetic fields flows at the same time from both terminals to the electric device. In AC circuits, individual electrons move back and forth in the wires and do not travel the entire circuit. Nevertheless, electric energy flows from the energy source to the device in the form of the fields.

Controlling electric current. The simplest way to stop a current flowing through a circuit is with a switch. A basic switch consists of two electric conductors that can be moved apart to create a gap in a circuit. When the switch is off, the gap is open, and no current flows. When the switch is on, the conductors are connected, and current flows.

Wires and electric devices become dangerously hot if too much current flows through them. Switches called fuses and circuit breakers protect the wiring in most buildings. If too many electric devices are plugged into an outlet, a fuse or circuit breaker will shut off the current. Many individual electric devices also contain fuses.

Sometimes people need to vary the strength of current, rather than merely turn it on or off. One way to adjust current strength is to vary resistance within the circuit. For example, turning the volume knob on a radio operates a variable resistor. This device adjusts resistance to the flow of current through the radio, making the sound louder or softer.

Switches and variable resistors cannot change currents quickly. Tiny semiconductor devices called transistors can be used to adjust current more rapidly. Transistors act as high-speed switches that turn on and off billions of times each second. Some devices contain millions of transistors on a single tiny chip of silicon, called an integrated circuit or simply a chip. Integrated circuits form the heart of computers, calculators, video games, and many other devices.

Electrically powered devices are said to be electronic if they carry electrical signals that can be varied in some way to represent information. Electronic devices include transistors, diodes, capacitors, inductors, and integrated circuits. Signals may represent sounds, pictures, numbers, letters, computer instructions, or other information. In the amplifier of a compact disc player, for example, transistors provide a continuous range of currents that strengthen electrical signals representing the sounds being played.

Electric shock is caused by an electric current passing through the body. The body's own electrical signals normally travel along nerves, carrying information to and from the brain. These electrical signals regulate the beating of the heart and other vital functions. Currents flowing through the body can disrupt these signals, causing muscle contractions, heart and respiratory failure, and death. Electric current can also burn skin and other body tissues.

Voltage measures the "push" that a source of electric energy supplies to move a charge through a circuit. The voltage of a flashlight or radio battery is usually too small to cause serious injury. But the 120 volts available at most household outlets could severely injure or even kill a person. The danger of electric shock is much greater when a person's skin is wet because water, mixed with salt from the skin, lowers the body's electrical resistance. A given voltage can then pass a greater current through the body.

Most electric devices have safety features to help prevent shock. Many appliances and tools have plugs with a third prong that connects the metal parts of the device to a wire leading to the ground. If the wiring inside the device becomes defective, the third prong usually causes the current to flow harmlessly to the ground.

Electrical dangers outdoors. If you climb a tree near an electric power line, you may get a shock if the tree touches the line. Storms sometimes knock down electric power lines. You could be injured or killed if you touch a fallen line when the power is still on.

Lightning discharges involve about 100 million volts. This voltage is more than enough to drive a current through the body that can kill a person. You can avoid being struck by lightning by staying indoors during a storm. If you get caught outdoors, stay away from open fields and high places. A forest is safer than open land. But do not stand under a tall or isolated tree, which is more likely to be struck. One of the safest places during a lightning storm is inside a car. If the vehicle is struck by lightning, its metal body will conduct the electric charge around the outside of the car, leaving the interior unharmed.

Electrical fire is another danger. When an electric current passes through a conductor, resistance causes the conductor to become hot. Sometimes the heat is desirable. For example, the wires in a toaster heat up to brown bread. But overheating in electrical cords or in household wiring can cause a fire. Electrical fires destroy many homes every year. To avoid fires, do not plug too many devices into the same outlet, and never use electric devices with worn or frayed cords.

Together, magnetism and electricity make a fundamental force of the universe called electromagnetism. Electromagnetism is based on the fact that the motion of electric charges can produce magnetic fields, and changing magnetic fields can produce electric currents.

For example, passing an electric current through a coil of wire makes the coil a temporary magnet called an electromagnet. The electric current creates a magnetic field around the coiled wire. As long as the current flows, the coil will be a magnet.

Magnetism can, in turn, produce an electric current by means of electromagnetic induction. In this process, a coil of wire moves near a magnet. This action causes an electric current to flow in the wire. The current flows as long as the movement continues. Generators produce electric current through this process.

Together, changing electric and magnetic fields make electromagnetic waves, also called electromagnetic radiation. These waves carry energy known as electromagnetic energy at the speed of light. Light, radio and TV signals, and microwaves all consist of electromagnetic waves. So do the infrared rays that you feel as heat when you stand near a hot stove, and the ultraviolet rays that cause sunburn. The X rays that doctors use to see inside your body are electromagnetic waves. The gamma rays that come from nuclear reactors and from outer space are also electromagnetic waves.

Other peoples, including the ancient Greeks and Chinese, knew of another substance that could attract things. It was a black rock called lodestone or magnetite. Today we know that it is a natural magnet. Lodestone attracts iron objects, which tend to be heavy. In contrast, amber attracts only light things, like straw. In 1551, the Italian mathematician Girolamo Cardano, also known as Jerome Cardan, realized that the attracting effects of amber and of magnetite must be different. Cardano was the first to note the difference between electricity and magnetism.

In 1600, the English physician William Gilbert reported that such materials as glass, sulfur, and wax behaved like amber. When rubbed with cloth, they too attracted light objects. Gilbert called these materials electrics. He studied the behavior of electrics and concluded that their effects must be due to some kind of fluid. Today, we know that what Gilbert called electrics are materials that are good insulators.

Experiments with electric charge. In the 1730's, the French scientist Charles Dufay found that charged pieces of glass attracted amberlike substances but repelled other glasslike substances. Dufay decided that there must be two kinds of electricities. He called them vitreous (for glasslike substances) and resinous (for amberlike substances). Dufay had found negative and positive electric charge, though he thought of them as two kinds of "electric fluid."

The American scientist and statesman Benjamin Franklin began to experiment with electricity in 1746. Franklin thought that there was only one kind of electric fluid. He theorized that objects with too much fluid would repel each other, but they would attract objects with too little fluid. If an object with an excess of fluid touched an object deficient in fluid, the fluid would be shared. Franklin's idea explained how opposite charges cancel each other out when they come in contact.

Franklin used the term positive for what he thought was an excess of electric fluid. He used the term negative for a deficiency of fluid. Franklin did not know that electricity is not a fluid. Rather, electricity is associated with the charges of electrons and protons. Today, we know that most positively charged objects actually have a deficiency of electrons, while negatively charged objects have an excess of electrons.

In 1752, Franklin performed his famous experiment of flying a kite during a thunderstorm. When the kite and string became electrically charged, Franklin concluded that the storm clouds were themselves charged. He became convinced that lightning was a huge electric spark. Fortunately, lightning did not strike Franklin's kite. If it had, he probably would have been killed.

In 1767, the English scientist Joseph Priestley described the mathematical law that shows how attraction weakens as the distance between oppositely charged objects increases. In 1785, the French scientist Charles Augustin de Coulomb confirmed Priestley's law. Coulomb showed that the law also held true for the repulsive force between objects with the same charge. Today, the principle is known as Coulomb's law.

In 1771, Luigi Galvani, an Italian anatomy professor, found that the leg of a recently killed frog would twitch when touched with two different metals at the same time. Galvani's work attracted much attention. In the late 1790's, Alessandro Volta, an Italian physicist, offered an explanation. Volta showed that chemical action occurs in a moist material in contact with two different metals. The chemical action results in an electric current. The flow of current had made Galvani's frog twitch. Volta gathered pairs of disks, consisting of one silver and one zinc disk. He separated the pairs with paper or cloth moistened with salt water. By piling up a stack of such disks, Volta constructed the first battery, called a voltaic pile.

Many experiments with Volta's battery and electric circuits followed. The German physicist Georg S. Ohm devised a mathematical law to describe the relationship between current, voltage, and resistance for certain materials. According to Ohm's law, published in 1827, a larger voltage can push a larger current through a given resistance. In addition, a given voltage can push a larger current through a smaller resistance.

Electricity and magnetism. In 1820, the Danish physicist Hans C. Oersted found that an electric current flowing near a compass needle will cause the needle to move. Oersted was the first to show a definite connection between electricity and magnetism. During the 1820's, Andre Marie Ampere discovered the mathematical relationship between currents and magnetic fields. That relationship, called Ampere's law, is one of the basic laws of electromagnetism.

In the early 1830's, the English scientist Michael Faraday and the American physicist Joseph Henry independently discovered that moving a magnet near a coil of wire produced an electric current in the wire. Further experiments showed that electrical effects occur any time a magnetic field changes. Audio and videotape recording, computer disks, and electric generators are based on this principle.

The Scottish physicist James Clerk Maxwell combined all the known laws covering electricity and magnetism into a single set of four equations. Maxwell's equations, published in 1865, describe completely how electric and magnetic fields arise and interact. Maxwell made a new prediction that a changing electric field would produce a magnetic field. That prediction led him to propose the existence of electromagnetic waves, which we now know include light, radio waves, and X rays. In the later 1880's, the German physicist Heinrich R. Hertz showed how to generate and detect radio waves, proving Maxwell correct. In 1901, the Italian inventor Guglielmo Marconi transmitted electromagnetic waves across the Atlantic Ocean, setting the stage for radio, TV, satellite communications, and cellular telephones.

The electronic age. The Irish physicist G. Johnstone Stoney believed that electric current was actually the movement of extremely small, electrically charged particles. In 1891, he suggested that these particles be called electrons. In 1897, the English physicist Joseph John Thomson proved the existence of electrons and showed that all atoms contain them. In research published in 1913, the American physicist Robert A. Millikan accurately measured the electron's charge.

In the late 1800's, scientists discovered that electrons can be dislodged from a metal surface in a vacuum tube. A vacuum tube is a glass tube with most of the air removed. The tube contains electrodes with wires that extend through the glass. Linking batteries to the electrodes causes a current of electrons to flow within the tube. The current can be modified by adjusting the voltage. Vacuum tubes can amplify, combine, and separate weak electric currents. This invention helped make radio, TV, and other technologies possible.

In 1947, the American physicists John Bardeen, Walter H. Brattain, and William Shockley invented the transistor. Transistors do the same jobs as vacuum tubes, but they are smaller and more durable, and they use far less energy. By the 1960's, transistors had replaced vacuum tubes in most electronic equipment. Since then, electronics companies have developed ever smaller transistors. Today, millions of interconnected transistors fit on a single chip called an integrated circuit.

Recent developments. Every year, the worldwide demand for electric energy increases. Most of the electric energy we use comes from power plants that burn fossil fuels, such as coal, oil, or natural gas. Some electric energy comes from nuclear and hydroelectric (water power) plants. Smaller amounts come from solar cells, windmills, and other sources.

Many people are concerned that the earth's supply of fossil fuel is limited and will someday run out. Another problem is that present methods of generating electric energy may harm the environment. In response, scientists, engineers, and power companies are trying to develop alternative sources of electric energy. Such sources may include solar, geothermal, wind, and tidal energy.

Many scientists hope that new electric devices will actually help curb the growing demand for electric energy. Computers, for example, can control the lights, air conditioning, and heating in buildings to reduce energy use. Compact fluorescent lamps, using miniature electronic circuits, provide the same light as ordinary light bulbs but use only one-fifth as much electric energy. Computers and modern communication systems enable people to work at home and save energy they would have used for transportation.

Contributor: Richard Wolfson, Ph.D., Prof. of Physics, Middlebury College.

See Electronics and Magnetism and their lists of Related articles.

Related articles include:

Biographies
Ampere, Andre Marie; Bell, Alexander Graham; Edison, Thomas Alva; Faraday, Michael; Hertz, Heinrich Rudolph; Latimer, Lewis Howard; Maxwell, James Clerk; Ohm, Georg Simon; Volta, Alessandro.

Basic principles of electricity
Atom; Electric Arc; Electric Circuit; Electric Current; Electric Field; Electric Power; Electromagnetism; Electromotive Force; Electron; Hall Effect; Inductance; Induction, Electric; Insulator, Electric; Ion; Lenz's Law; Matter; Molecule; Ohm's Law; Proton.

Creating and controlling electric energy
Armature; Battery; Capacitance; Circuit Breaker; Electric Eye; Electric Generator; Electric Switch; Electrode; Electrolysis; Electrolyte; Fuel Cell; Fuse; Induction Coil; Leyden Jar; Magnetic Amplifier; Magneto; Piezoelectricity; Solar Energy; Thermocouple; Transformer; Turbine; Van de Graaff Generator.

Measuring electric energy
Ammeter; Ampere; Coulomb; Electric Measurement; Electric Meter; Electroscope; Farad; Galvanometer; Henry; Joule; Kilowatt; Ohm; Oscilloscope; Potentiometer; Volt; Voltmeter; Watt; Wattmeter; Wheatstone Bridge.

Uses of electric energy
Cable; Clock; Electric Car; Electric Furnace; Electric Light; Electric Motor; Electric Railroad; Flashlight; Linear Electric Motor; Microphone.

Other related articles
Electric Eel; Electric Fish; Electric Ray; Electrocution; Electromotive Series; Energy; Light; Lightning; Lightning Rod.

If an atom has more protons than electrons, what kind of charge will the atom have?

How are insulators important to electrical safety?

What device produces electric energy by chemical action?

Why does metal conduct electric current better than wood?

How are electricity and magnetism related?

What familiar office machine uses static electricity?

How can you make a balloon stick to your shirt? Why does it stick?

What should you do if you are caught outdoors during a lightning storm?

How has electric energy changed the way people live?

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Glover, David. Batteries, Bulbs, and Wires. Kingfisher Bks., 1993.

Parker, Steve. Electricity. Dorling Kindersley, 1992.

Hall, Dorothea, ed. Electricity: A Step-by-Step Guide. Smithmark, 1993.

Middleton, Robert G. Practical Electricity. 4th ed. Ed. by L. Donald Meyers and J. A. Tedesco. Macmillan, 1988.

Nye, David E. Electrifying America. MIT Pr., 1990.

Wong, Ovid K. Experimenting with Electricity and Magnetism. Watts, 1993.

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