How An Electric Bulb Is Illuminated?
An Englishman Humphry Davy in the year 1800, was conducting certain experiments with electricity. He had electric battery which was quite weak. He connected the two wires to the ends of battery and attached a piece of carbon to each of the free ends of the wires. By touching the two slightly apart, he produced a sizzling light.
This was called “an electric arc”, but it was the first evidence that electric light was possible. He replaced the two carbon pieces with a thin platinum wire connecting the two ends of the wires leading to the battery. When the electric current passed through it, the wire got heated, began to glow and emitted light.
The source of electricity in this case was not strong enough. A student of Davy’s Michael Faraday, further conducted experiments that lead to the development of electric generators. By using steam engines to drive the generators, better sources of electricity were found.
In the United States, Thomas Edison, conducted experiments with thin thread of carbon. When carbon filament was heated by passing electric current through, it glowed. If this was done in air, the carbon itself got burnt. So, Edison decided to place it in a glass bulb and pumped air out of it. In absence of Carbon it would not glow. It glowed brightly and only wasted away very slowly. Now we had an electric bulb that gave pretty good light.
The scientists knew that the more a filament was heated, the more light it gives. So, they searched a material that could be heated to high temperatures without melting itself. One of these is tantalum a metal that melts at 2950 degrees centigrade. It was drawn into fine wires and used in lamp filaments in the year 1905.
Still a better metal for filaments is tungsten. It melts at 3370 degrees centigrade. Initially, it was found difficult to draw this metal into wires, but in years it became possible. Today tungsten filaments are used in electric Lamps. Only in the United states about 1,000,000,000 of these are made each year.