The role of the gas is to prevent evaporation of the filament, without introducing significant heat losses. For these properties, chemical inertness and high atomic or molecular weight is desirable. The presence of gas molecules knocks the liberated tungsten atoms back to the filament, reducing its evaporation and allowing it to be operated at higher temperature without reducing its life (or, for operating at the same temperature, prolongs the filament life). It however introduces heat losses (and therefore efficiency loss) from the filament, by heat conduction and heat convection. COUNT 4
QSN1 What is a potential problem with the use of gas in a light bulb? ANS1 introduces heat losses (and therefore efficiency loss) QSN2 What are the ideal chemical properties for the gas in a light bulb? ANS2 chemical inertness and high atomic or molecular weight QSN3 What is the purpose of the gas in a light bulb? ANS3 to prevent evaporation of the filament, without introducing significant heat losses QSN4 How do gases prevent evaporation of the filament? ANS4 The presence of gas molecules knocks the liberated tungsten atoms back to the filament