An electric lamp is a gllas bulb, often filled with nitrogen or some other chemically inactive gas containing a wire or filament usually made of tungsten in which the passage of an electric current through the filament heats it to a white heat and then to the visible radiation i.e. light.
There are types of lamps for producing light by electricity. Incandescent lamp, b) Electric arc lamp and c) Gas discharge lamp.
The incandescent or filament type consists of a file metallic wire of high resistance known as filament enclosed in an evacuated glass globe. When the electric current passes through the filament, heat is produced and the temperature of the filament increases. At high temperature, it radiates heat as well as light energy thereby producing electric lights by incandescence of a heated filament.
The two types of incandescent lamps are - (a) Metal filament lamps & (b) Carbon filament lamps.
It should have high melting point, low vapour pressure, high resistivity and low-temperature coefficient. It should be ductile and mechanically very strong to withstand vibrations during normal use.
Tungsten, Tantalum and Carbon.
Tungsten is widely used for the filament of the incandescent lamp due to its high-temperature co-efficient, high melting point, low vapour pressure, ductility and good mechanical strength.
Melting point is 3400°C and working temperature is about 2000°C.
(a) Straight wire type, (b) Coiled type and (c) Coiled-coil type.
The causes are as follows :-
Incandescent lamp works by the heating effect of electricity.
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