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Why is an electric incandescent bulb filled with argon gas? State any disadvantage of the practice.


The temperature of the tungsten filament of an incandescent bulb rises to more than 20000C when it is in operation. At this high temperature the atoms of tungsten vapourise and settle on the glass bulb. This in turn blackens the bulb and reduces the light output. To overcome this problem, incandescent bulbs are filled with a mixture of nitrogen and argon gases at very low pressure. When current passes through the filament, a sort of convection current is set up within the glass bulb which carries the spurting tungsten particles upward. Thus, the blackening of the lower part of the bulb is prevented. It also regulates the operating temperature of the filament & the glass bulb. Gas filling of the incandescent bulb causes convection current while the bulb is in operation.This convection current rapidly takes away the heat from the heated filament. Hence temperature of the filament drops reducing the light output to some extent. This problem is, however, encountered by using coiled coil filament.

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