Before 1878, we were using lamp as source of light during night. During Kingdoms of kings, crude oil was boon for soldiers to find path in dark night during wars; flambeau was the only torch available in that era. Then the revolution took placed in 1878, by the greatest Physicist named Sir Thomas Alva Edison. After 1000 unsuccessful attempt finally he succeeded and produced first incandescent bulb, which can give light energy at least for 12 hours.
Electric bulb works on the principle of heating effect of electric current. We know that when current flow through wire, it gets heated. Due to this heat material of wire start changing its colour. (You must have seen blacksmith making iron instrument by heating iron block at higher temperature. Iron block get reddish in colour and become soft, then using hammer he gives the desired shape to the instrument. That means metals can change its colour when get heated.) This property of material is useful as source of light during night. Different metals produce different colours after heating. Most preferred colours for vision are yellow and orange, which can get by heating thin wire of tungsten metal (thin wire of tungsten metal is called filament.) See the diagram below indicates the structure of bulb.
The filament used here is made of tungsten whose melting point is around 34000C. When current passes through this filament, its temperature start rises and colour also changes to yellowish orange. This yellow colour emitted by filament of tungsten used as sources of light during darkness of night. The glass coating is provided with noble gas so that the heat produced in the bulb can get absorbed.
This bulb consumes large power so that they are not cost effective, so alternatives for such bulbs were necessary. Hence in modern time we use new generation halogen light bulbs, fluorescent tubes, compact fluorescent light bulbs (CFLs), LEDs etc, which are more brighter, can produce white light also, and affordable as well.
Q. What was the source of light to find path for soldiers during war?
Ans: Flambeau.
Q. Who invented first electric bulb?
Ans: Sir Thomas Alva Edison
Q. What is the principle of working of electric bulb?
Ans: It works principle of heating effect of electric current.
Q. Which material is used for making filament of electric bulb?
Ans: Tungsten.
Q. What colour is emitted by tungsten filament due to heat?
Ans: yellowish orange.
Q. What is melting point of filament in bulb?
Ans: Around 34000C.