An incandescent light bulb is an electric light with a tungsten wire filament heated to a high temperature by passing an electric current through it until it glows with visible light. The hot filament is protected from oxidation with a glass bulb that is evacuated (vacuum). Incandescent bulbs are known to be rather inefficient forms of lighting, typically converting less than 5% of the energy they consume into visible light. Higher efficiencies can be achieved by increasing the filament temperature, but this is typically associated with reduced lifespan of the filament. Explain how heat is transferred (which modes) from the hot tungsten filament surface of the incandescent light bulb shown below to the ambient air in the room. (Neglect heat transfer through the threaded portion of the light bulb). Some light bulbs are filled with an inert gas rather than being evacuated. How would you expect this to affect the filament temperature and consequently the light bulb efficiency, and why? Some light bulbs are filled with an inert gas rather than being evacuated. How would you expect this to affect the filament temperature and consequently the light bulb efficiency, and why?
Electricity passes through tungsten coil. The coil gets heated acording to Joule heating ( I^2Rt), where I is current, R is resistance and t is time. Incandescence occurs when electrical resistive heating creates thermally excited atoms. Some of the thermal kinetic energy is transferred to electronic excitations within the solid. The excited states are relieved by photonic emission. When enough of the radiation emitted is in the visible spectrum so that we can see an object by its own visible light, we say it is incandescing. In a solid, there is a near-continuum of electron energy levels, resulting in a continuous non-discrete spectrum of radiation. To emit visible To emit visible light, a solid must be heated red hot to over 850 K.
b) As Argon is filled in the bulb, pressure inside the bulb increases. Therefore, temperature is reached with lesser efforts. This makes the evaporation temperature of Tungsten higher and the rate of evaporation is drastically decreased due to fill in Argon.
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