Thursday, January 05, 2006

History of Electricity and Magnetism

The history of development of physics of electricity and magnetism is very old and interesting.

In 600 B.C., the Greek philosopher, mathematician and astronomer, Thales of Miletus (636-546 B.C.) observed that amber, when rubbed with silk aquires special properties - produces sparks and attracts small pieces of straw. The commonly used words electricity, electron etc. come from the greek name for amber, elektron. Thales also observed that pieces of magnetic rock called loadstone also have such powers. The words magnet and magnetism etc. come from the name of the place called Magnesia where loadstone was found.

The study of Electric and Magnetic phenomena remained almost univestigated for a long time after this.

William Gilbert (1540-1603) of England carried out systematic experiments related to electricity and magnetisms and described them in his famous book, De Magnete. He recognized that earth was a huge magnet. The invention of the electroscope is credited to him. Electroscope is an instrument useful for observing electrostatic effects.

The American Scientist Benjamin Franklin(1706-1790), famous for his kite-experiment, established the law of conservation of charge and discovered that there are two kinds of charge. He also invented the lightning rod.

Charles Augustin de Coulomb (1736-1806) performed measurements of electric and magnetic forces with a delicate torsion balance he had himself invented. He came up with the famous Coulomb's Law which gives the magnitude of force between two point charges.

F = kq1q2/r2
F is the Force
q1and q2 are the values of the two point charges,
r is the separation between them.
k is a constant of proportionality

The unit of charge Coulomb(C) is named in his honour.

The production of electric currents was achieved by Alessandro Volta (1745-1827) of Italy around the year 1800. He invented the voltaic cell and the electric battery by connecting the cells in series. The unit of potential (Volt, V) is named in his honour.

The famous Gauss theorem in vector calculus (also known as the Divergence theorem) was formulated by the gifted German mathematician Karl Friedrich Gauss (1777-1855) around this time. The unit of Magnetic Field Strength (gauss, G) is named in his honour.

A vital event in the history of electricity and magnetism took place in 1819. Hans Christian Oersted (1777-1851), a Danish Professor of Physics discovered that a curent carrying wire caused a nearby compass needle to deflect. This was the first time when a link was found between electric and magnetic phenomena. Before this, electricity and magnetism were studied as independent phenomena.

In 1820, the French Physicist Andre Marie Ampere (1775-1836) invented the solenoidal coil. Solenoidal coils can produce magnetic fields. Ampere proposed that atoms are magnetized by tiny electric currents circulating in them. The unit of electric current (ampere, A) is named in his honour.

Georg Simon Ohm (1787-1854)of Germany gave his famous law known as the Ohm's law relating the voltage, current and resistance of a conductor. The unit of resistance (ohm) is named in his honour.

Under identical external conditions, for a conductor

V = RI

V is the potential difference across the ends of the conductor
I is the electric current flowing in the conductor
R is the resistance of the conductor

This law of Ohm was not readily accepted initially.

That electricity could produce magnetic effects was demonstrated by Oersted as seen above, when an electric current caused deflection of a compass needle. The reverse phenomena, i.e., the production on electricity through magnetism was discovered by Michael Faraday (1791-1867) of London in 1831. Faraday observed that a changing magnetic field could produce an electric current. The unit of capacitance (Farad, F) is named in his honour. Also, the amount of charge on one mole of electrons, i.e. 96,000 coulomb is given the name Faraday.

The above effect, that is production of electricity by a changing magnetic field was observed independently by Joseph Henry of New York. The Electric Telegraph and Relay were invented by Henry. The unit of Inductance (Henry, H) is named in his honour.

A unification of the many laws of electricity that had been discovered was to come with the physicist James Clerk Maxwell (1831-1879), a professor at Cambridge University, England. He published a unified theory of electromagnetism in 1873. His equations show in an elegant manner the interdependence of electricity and magnetism. He postulated that light is an electromagntic wave and electromagnetic waves exist for other wvaelength than known for light. However, his work did not receive immediate acceptance. Physicists of the time were skeptical of his theories.

It was Heinrich Hertz (1857-1894) in 1888 who demonstrated the existence of electromagnetic waves. Hertz was a professor of physics at Karlsruche, Germany. He generated and detected radio waves and showed that their behavior was similar to that of light.

A sensation was created by Guglielmo Marconi (1874-1931) in 1901 by sending radio signals across the atlantic ocean. He applied the laboratory experiments of Hertz to practical appliations. Marconi developed radio communication for ships. With this, ships, when at the sea, were no longer in complete isolation. Now they could be in contact with people on land. The radio, thus, became very popular and important.

The American inventor Thomas Alva Edison (1847-1931) put electricity and magnetism to extensive use. He made several inventions in the fields of telegraphy, lighting and power generation. He is popularly known as the inventor of the light bulb.

Nikola Tesla (1856-1943) developed the induction motor. He was an advocator of the use of alternating current for transmission and distribution of electricity. He designed the power generating system at Niagra falls.The unit of Magnetic Field (Tesla, T) in named in his honour.

In 1905, the great physicist Albert Einstein (1879-1955) theorized his famous theory of relativity. The theory tells us that the manifestation of the electric field or magnetic field depends upon the motion of the observer.

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