How is light produced by an electric bulb?

The moment we switch on an electric bulb in a dark room in the night, the whole room is illuminated with light and all the articles kept there become clearly visible. Do you know how light is produced from the bulb?

The first electric bulb of the world was developed by the American scientist Thomas Edison in the year 1878. In making this bulb, he utilized the principle that light and heat are produced when electricity is passed through wires. Actually the electric bulb converts electrical energy into heat and light energy. Such light sources are called ‘incandescent lamps’. To begin with, a coil of very fine platinum wire was sealed in a glass bulb used by Edison. When the two ends of this coil were connected to the electric supply, it became red hot and started glowing. Lamps made by Edison could not become popular because platinum wires were very costly.

Subsequently, many changes were made in the filament materials used in the electric bulbs. For some time carbon filaments were used Later on, filaments made up of tungsten and tantalum metals came into use. Since the melting points of these metals are very high, filaments made from them do not easily burn out. 

In the modern electric bulb, the coiled tungsten filament is sealed in a glass bulb. Each end of the filament is welded to a thick wire. These thick wires pass through a glass pillar. Two ends of these wires are soldered with contact pads. To prevent the two ends from coming in contact with each other, insulating material is filled in the metal cap. The air inside the glass bulb is removed and filled with a mixture of argon and nitrogen gases. Thus it prevents the evaporation of metal from the filament and protects it from melting. This mixture also increases the efficiency. When electric current flows through the filament, it first becomes red hot and then white. This glowing white filament gives us the light. The power of a bulb is measured in watts.

While handling a bulb, we should not shake it because the filament is likely to break due to the jerks. Once the filament is broken, the bulb becomes useless. While fixing bulbs in their holders, one should keep the relevant switches off to avoid any possibility of electric shocks.



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