# Electricity, Its Past and Present Development +

## Electricity and magnetism were long thought to be separate forces

It was not until the 19th century that these two forces were finally treated as an interrelated occurrence.

On a practical level, electric and magnetic forces function quite differently and are described with different equations; for example, electric forces are produced by electric charges either at rest or in motion while magnetic forces are produced only by moving charges and act on charges in motion.

The electric force is responsible for most of the physical and chemical properties of atoms and molecules.

It is considerably stronger compared with gravity; for example, the absence of only one electron out of every billion molecules in two 70-kilogram (154-pound) people standing two meters (two yards) apart would repel them with a 30,000-ton force.

On a more familiar scale, electric circumstances are responsible for the lightning and thunder that goes with certain storms.

### Everyday modern life must deal with electromagnetic phenomena

When a light bulb is switched on, a current flows through a thin filament in the bulb; the current heats the filament to such a high temperature that it glows, illuminating its surroundings.

Electric clocks and connections link simple devices of this kind into complex systems; such as, traffic lights that are timed and synchronized with the speed of vehicular flow.

Radio and television sets receive information carried by electromagnetic waves traveling through space at the speed of light.

To start an automobile, currents in an electric starter motor generate magnetic fields which rotate the motor shaft and drive engine pistons to compress an explosive mixture of gasoline and air; the spark initiating the combustion is an electric discharge, which makes up a momentary current flow.

Electric current is a measure of the flow of charge, as, for example, charge flowing through a wire. The size of the current is measured in amperes and an ampere of current represents the passage of one coulomb of charge per second, or 6.2 billion billion electrons per second.

A current is positive when it is in the direction of the flow of positive charges while its direction is opposite to the flow of negative charges.

### Electric and magnetic forces have been known since antiquity, but they were regarded as separate events for centuries.

Magnetism was studied experimentally at least as early as the 13th century because the properties of the magnetic compass undoubtedly created an interest in the observable events.

Systematic investigations of electricity were delayed until the invention of practical devices for producing electric charges and currents.

As soon as inexpensive, easy-to-use sources of electricity became available, scientists produced a wealth of experimental data and theoretical insights.

As technology advanced, they also studied magnetism and electrostatics, electric currents and conduction, electrochemistry, magnetic and electric induction, the interrelationship between electricity and magnetism, and finally the fundamental nature of electric charges.

### Early observations and applications

The ancient Greeks knew about the attracting forces of both magnetite and rubbed amber. Magnetite, a magnetic oxide of iron mentioned in Greek texts as early as 800 B.C., was mined in the province of Magnesia in Thessaly.

Thales of Miletus, who lived nearby, may have been the first Greek to study magnetic forces. He apparently knew that magnetite attracts iron and that rubbing amber (a fossil tree resin that the Greeks called ēlektron) would make it attract such lightweight objects as feathers.

According to Lucretius, the Roman author of the philosophical poem De rerum natura ("On the Nature of Things") in the 1st century B.C., the term magnet was derived from the province of Magnesia.

Pliny the Elder, however, attributes it to the supposed discoverer of the mineral, the shepherd Magnes, "the nails of whose shoes and the tip of whose staff stuck fast in a magnetic field while he pastured his flocks".

The oldest practical application of magnetism was the magnetic compass, but its origin remains unknown.

Some historians believe it was used in China as far back as the 26th century B.C.; others maintain that it was invented by the Italians or Arabs and introduced to the Chinese during the 13th century A.D.

### In the United States, Benjamin Franklin sold his printing house, newspaper, and almanac to spend his time conducting electricity experiments

In 1752 Franklin proved that lightning was an example of electric conduction by flying a silk kite during a thunderstorm.

He collected electric charges from a cloud by means of wet twine attached to a key and thence to a Leyden jar, then he used the accumulated charge from the lightning to perform electric experiments.

### Electricity took on a new importance with the development of the electric motor

A machine, which converted electric energy to mechanical energy, became an integral component of a wide assortment of devices ranging from kitchen appliances and office equipment to industrial robots and rapid-transit vehicles.

Although the principle of the electric motor was devised by Faraday in 1821, no commercially significant unit was produced until 1873. In fact, the first important AC motor, built by the Serbian-American inventor Nikola Tesla, was not demonstrated in the United States until 1888.

Tesla started producing his motors in association with the Westinghouse Electric Company a few years after DC motors had been installed in trains in Germany and Ireland.

By the end of the 19th century, the electric motor had taken a recognizably modern form. Subsequent improvements have rarely involved radically new ideas; however, the introduction of better designs and new bearing, armature, magnetic, and contact materials has resulted in the manufacture of smaller, cheaper, and more efficient and reliable motors.

### The modern communications industry is among the most spectacular products of electricity

Telegraph systems that were using wires and simple electrochemical or electromechanical receivers developed extensively in western Europe and the United States during the 1840s.

An operable cable was installed under the English Channel in 1865, and a pair of transatlantic cables were successfully laid a year later. By 1872 almost all of the major cities of the world were linked by telegraph.

Alexander Graham Bell patented the first practical telephone in the United States in 1876, and the first public telephone services were operating within a few years.

In 1895, the British physicist Sir Ernest Rutherford advanced Hertz’s scientific investigations of radio waves and transmitted radio signals for more than one kilometer.

Guglielmo Marconi, an Italian physicist and inventor, established wireless communications across the Atlantic employing radio waves of approximately 300 meter to 3,000 meter wavelength in 1901.

Broadcast radio transmissions were established during the 1920s.

Telephone transmissions by radio waves, the electric recording and reproduction of sound, and television were made possible by the development of the triode tube.

This three-electrode tube, invented by the American engineer Lee De Forest, permitted for the first time the amplification of electric signals.

Known as the Audion, this device played a significant role in the early development of the electronics industry.

Until 1939, the electronics industry was almost exclusively concerned with communications and broadcast entertainment.

Scientists and engineers in Britain, Germany, France, and the United States did initiate research on radar systems capable of aircraft detection and antiaircraft fire-control during the 1930s; however, and this marked the beginning of a new direction for electronics.

During World War II and after, the electronics industry made strides paralleled only by those of the chemical industry. Television became commonplace; and a broad array of new devices and systems, most notably the electronic digital computer, emerged.

The electronic revolution of the last half of the 20th century has been made possible in a large part by the invention of the transistor (1947) and such subsequent developments as the integrated circuit.

This miniaturization and integration of circuit elements has led to a remarkable decrease in the size and cost of electronic equipment and an equally impressive increase in its reliability.

—Compiled from excerpts located at
"Electromagnetism", Encyclopædia Britannica Online; July 15, 2010.

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