MadSci Network: Physics

Re: How does a light bulb work?

Area: Physics
Posted By: Matthew Barchok, High School Junior, none
Date: Thu May 22 20:30:08 1997
Area of science: Physics
ID: 863548257.Ph

A light bulb is really quite simple. Have you ever seen pictures of molten steel being poured? If you have, you will notice that it is glowing white-hot. A light bulb is simply a small metal wire that is glowing with heat. In this case, the metal is tungsten (W on the Periodic Table). This is important because tungsten is solid at very high temperatures. A light bulb also has most of the air sucked out of it. If it didn't, the wire would actually burn up instantly. When a light bulb "burns out", it is because the filament slowly vaporizes; the black on the inside of a burned out lightbulb is really just resolidified metal vapor.

Now back to how a lightbulb works. Electricity flowing through the wire causes it to heat up. This heat makes it glow. It heats up because of a concept called resistance. When electricity passes through something, the substance it is passing through tries to hold on to the electrons. The electrons have to be forced through. Some of this force is absorbed by the metal and given off as heat. As the filament heats up, it gives off light.

If you don't understand this next part, its O.K., we didn't learn it until tenth grade.

The heat energy goes into electrons of the tungsten atoms. The energy pushes the electrons farther away from the nucleus of the atoms. As the electrons fall back, they give off photons, little bits of light.

Fluorescent light bulbs work similarly. Electricity moves in pulses through a tube. The electricity hits special molecules inside the tube and their electrons are knocked away. As their electrons fall back, light is given off. In this case, the electrons are knocked off by electrictiy, not heat, and therefore, fluorescent light bulbs can be cooler. Since they are cooler, nothing vaporizes, and the fluorescent light bulb lasts longer.

I hope I answered your question without confusing you too much.

Keep those questions coming!

Matthew Barchok, Mad Scientist.

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