Our light bulb burnt out the other day, and it got me curious…why do light bulbs burn out anyway!?

“There are a number of sites that describe in detail how a bulb works. HowStuffWorks and How Things Work both do a thorough job of explaining the physics of this watershed invention.

To summarize: electrical current flows through the bulb’s filament, a long, super thin, double coil wire made of the metal tungsten. This interaction creates extreme heat around 4,000 degrees and starts a process that causes the atoms to release extra energy in the form of light photons.

At such a high temperature, though, some tungsten atoms will fly off and collect on the inside of the bulb’s glass. This loss of tungsten is slowed but not prevented by adding inert gases, typically argon. The argon atoms rebuff the tungsten atoms when they collide, so that some tungsten atoms rebound and rejoin the solid filament. But eventually, as more and more atoms are lost, the filament starts to disintegrate.

The filament is further compromised by the rapid heating and cooling of the wire when the bulb is turned on and off. This creates areas of stress almost like in a paper clip that’s repeatedly bent. Eventually, this stress, coupled with the loss of tungsten atoms, weakens the filament enough to break. And that’s when it’s time to fork over another couple of bucks to GE.”

taken from: http://ask.yahoo.com/20041228.html