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Light bulb question

  1. Sep 22, 2007 #1
    Why does passing current through Wolfram filament, heats the Wolfram filament in light bulb? What happens with the electrons?
     
  2. jcsd
  3. Sep 22, 2007 #2
    It's down to Ohmic heating. The electrons collide with the ions of the filament, and pass on its kinetic energy to the ions in the form of heat energy, which is proportional to the square of the current multiplied by the resistance of the filament.
     
  4. Sep 22, 2007 #3
    And why lets say, the Wolfram filament is releasing more energy (when current passes through it) than the iron?
     
  5. Sep 22, 2007 #4

    Danger

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    Welcome to PF, Yyouth.
    First off, thank you too much for driving me half nuts with your question. :grumpy: (:biggrin:) I spent a couple of hours trying to figure out who the hell Wolfram was and how his filament differed from a normal tungsten one. :rolleyes:
    Anyhow, tungsten is a lot denser than iron, so internal particle collisions are far more numerous. Its other properties, though, are what make it so incredibly perfect for lightbulb use. To start with, it has one of the highest melting points of any metal. Combined with its very low thermal expansion coefficient, it allows bulbs to be run far hotter than could be achieved with other materials. That low expansion also allows a very long piece of wire to be put into a very small space. Filaments are typically double-coiled, wherein the original coiled wire is coiled again. The easiest way that I can think of to clarify that is if you were to take a long spring such as from a ball-point pen and wrap it around a toothpick. That 1/4" long filament would probably be over a metre long if stretched out. Tungsten is also very unreactive, so impurities that might sneak into the argon atmosphere of a bulb are less likely to cause failure.
     
  6. Sep 22, 2007 #5
    Hey.. this not a reply because im new i this forum.... i need help..... how can i post a questions...... sorry for the trouble...
     
  7. Sep 22, 2007 #6

    Danger

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    Welcome to PF, Cundo.
    Go to the appropriate sub-forum (Classical Physics is this one). Just above the main body, there's a button that says 'New Thread'. Click on that, and you'll be prompted to enter a title and whatever text you want. When you're satisfied with your post, click on the 'Submit' button at the bottom. If you're unsure of what sub-forum it belongs in, post it in General Discussion and a Mentor will move it to where it should be.
     
  8. Sep 22, 2007 #7
    Thankss.... i got a feeling ill be listening from you again...
     
  9. Sep 22, 2007 #8

    Danger

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    Don't let it become a habit; I make up half of the stuff that I post here. :wink:
     
  10. Sep 22, 2007 #9
    Ok, thank you very much.
     
  11. Sep 22, 2007 #10
    And when the element will be turned into liquid? Should the atoms be totally disintegrated?
     
    Last edited: Sep 22, 2007
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