Does the thickness of a filament affect its glow? HELPP!!!

[longvietxx]

hi guys i really need help. My science project is due on December 14, 2009 ,and i have very little imformation.

Topic: What is the effect of the thickness of a filament on its glow?

(filament refering to light bulbs)

Thank you,
Long

[deleted-71588]

Part of coming up with a good Science Fair project is coming up with a testable hypothesis that can be done with the equipment and materials you can come up with in the time frame.

Light bulbs provide a partial vaccum with a means of eliminating all oxygen so that the filament does not immediately oxidize and burn up immediately.

Unless you have vaccum pumps and ways to eliminate oxygen and means to fabricate filaments, you are going to have a difficult time in actually doing any physical experiments. I'm not sure that light bulb manufacturers provide any technical data on their filaments. For most uses, the electrical properties, the type of connector, the amount of light produced, expected services hours, physical bulb shape and size are the things that matter.

The resistance properties of different thickness filaments will also make it difficult to determine the effect of filament thickness on glow without introducing other differences into the problem. With all resistive materials, the smaller the cross section, the more resistance per length. The smaller the cross section, the less current the filament can tolerate without over heating. The color and light properties will be significantly affected by temperature of the filament.

You might want to come up with a different project and testable hypothesis.

[deleted-71709]

I agree with Craig's advice. This is a very difficult and complicated hypothesis to prove experimentally. You should consider something less complicated if you need to complete it in just 3 weeks.

If, however, you're really interested in this topic, here is an interesting exchange of ideas I found: http://www.physicsforums.com/archive/in ... 10237.html

Good luck with whatever you select for your project.

Ed Neu
Buffalo, MN

[rmarz]

I agree with the other experts, but I'm not sure what your hypothesis is. By 'glow' I assume you mean the intensity of the light? There are two factors to consider. One is the color temperature of the light. Light bulbs are driven to near destructive temperatures to achieve a very high filament temperature, therefore a very high value of photon output. That would be measured as light intensity on a light meter. (That is the reason that the bulb is evacuated and backfilled with inert gas. In an oxygen bearing environment, the filament would quickly oxidize and burn up.) If you assume that we would drive any size tungsten filament to the same temperature, the larger the surface area of the filament (larger diameter of filament wire) the more light value we would measure at any distance. This is a luminosity figure. I think you know what you want to achieve, but it would be difficult for you to create the appropriate test samples. A little more thought and you might come up with a subset of an experiment that you can more easily demonstrate.

Rick Marz