Filament, lightbulb

The radiation emitted by bodies at room temperature falls inlo the infrared region of the spectrum, which extends from 0.76 to 100 p,ni. Bodies start emitting noticeable visible radiation at temperatures above 800 K. The tungsten filament of a lightbulb must be heated to temperatures above 2(XX) K before it can emit any significant amount of radiation in the visible range. 

I The temperature of the filament of an incandescent lightbulb is 2500 K. As-I suming the filament to be a blackbody, determine the fraction of the radiant energy emitted by the filament that falls in the visible range. Also, determine I the wavelength at which the emission of radiation from the filament peaks. 

SOLUTION the temperature of the filament of an incandescent lightbulb Is given. The fraction of visible radiation emitted by the filament and the wavelength at vdiich the emission peaks are to be determined. 

An incandescent lightbulb is desired to emit at least 15 percent of its energy al wavelengths shorter than 0.8 pm. Determine the minimum temperature to which the filament of the lightbulb must be heated. 

Suppose an ordinary lightbulb were filled with air. When the bulb is turned on, an electric current runs through the metal filament (wire) inside the bulb. The filament gets very hot, begins to glow, and gives off light. 

An easy solution to that problem is to use nitrogen instead of ordinary air in the lightbulb. Nitrogen does not react with other elements very well, even when they get hot. The filament can get very hot, but the metal of which it is made will not combine with nitrogen gas. The nitrogen gas is an inert atmosphere for the bulb. 

The tungsten filament in an incandescent lightbulb ordinarily operates at a temperature of about 2500°C. At this temperature, the vapor pressure of solid tungsten is 7.0 X 10 atm. Estimate the number of gaseous tungsten atoms per cubic centimeter under these conditions. 

Use Control rods in water-cooled nuclear reactors lightbulb filaments, electrodes, special glasses, getter in vacuum tubes. 

Incandescent lightbulbs are filled with noble gases, usually argon and krypton, to protect the filament. The tungsten filament gets so hot that it will react with all but the most inert elements. 

Tungsten (W) is used as a filament in incandescent lightbulbs because it has a high melting point, 3420°C, and boiling point, 5850°C. But, nothing lasts forever. Because electricity continuahy passes through the filament, the metal eventuahy breaks as it vaporizes, and the bulb burns out. 

If a lightbulb were filled with air, the filament would react with oxygen, burn, break, and lose its ability to provide light. If there were no gas inside the bulb, the filament would quickly vaporize and no electricity would flow. 

Evaluate Why does a tungsten filament last longer in a halogen lightbulb than in a normal lightbulb ... 

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