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Thread: light bulb question

  1. #1 light bulb question 
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    Why does passing current through Wolfram filament, heats the Wolfram filament in light bulb? What happens with the electrons?


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  3. #2  
    Forum Masters Degree bit4bit's Avatar
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    Wolfram filament? Can't say I've heard that term before.

    The heating of any conductor due to current is the result of collisions of the free electrons, as they flow through the lattice, with its constituent ions.

    Increasing the length, or current, or decreasing the width of the filament will result in more collisions, because more electrons are confined to flow within a smaller cross-sectional area, or longer length.

    The energy transfer goes like this; the free electrons gain kinetic energy due to their acceleration by the electric field (a result of a potential difference), upon a collision with an ion, this kinetic energy is transferred to the ion, increasing the vibrational energy of the lattice, and hence the temperature of the conductor. If there were no collisions, then only an initial potential difference would need be applied, but since this is not the case, then for a current to flow, the p.d. must be sustained.

    This is the heating effect of current.


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    Quote Originally Posted by bit4bit
    Wolfram filament? Can't say I've heard that term before.

    The heating of any conductor due to current is the result of collisions of the free electrons, as they flow through the lattice, with its constituent ions.

    Increasing the length, or current, or decreasing the width of the filament will result in more collisions, because more electrons are confined to flow within a smaller cross-sectional area, or longer length.

    The energy transfer goes like this; the free electrons gain kinetic energy due to their acceleration by the electric field (a result of a potential difference), upon a collision with an ion, this kinetic energy is transferred to the ion, increasing the vibrational energy of the lattice, and hence the temperature of the conductor. If there were no collisions, then only an initial potential difference would need be applied, but since this is not the case, then for a current to flow, the p.d. must be sustained.

    This is the heating effect of current.
    And why lets say, the Wolfram filament is releasing more energy (when current passes through it) than the iron?
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  5. #4  
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    Wolfram is the element that we English-speakers call tungsten, symbol W. German speakers call it Wolfram.

    I think that Scientist91 may be asking why do we make filaments out of Wolfram (tungsten) rather than iron. The answer is that Wolfram/tungsten has a much higher melting point than iron. Both metals can be heated electrically until they are white hot. Iron would melt but Wolfram/tungsten remains solid.

    If I missed your question, please say it again.
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    Quote Originally Posted by SteveF
    Wolfram is the element that we English-speakers call tungsten, symbol W. German speakers call it Wolfram.

    I think that Scientist91 may be asking why do we make filaments out of Wolfram (tungsten) rather than iron. The answer is that Wolfram/tungsten has a much higher melting point than iron. Both metals can be heated electrically until they are white hot. Iron would melt but Wolfram/tungsten remains solid.

    If I missed your question, please say it again.
    Ok, thanks.
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    an important part of a light globe is the gas that surrounds the tungsten filiment. argon or nitrogen are what is mostly used, because they are noble gasses and as such don't easily react with other elements. if normal air was used, the tungsten would quickly react with the oxigen in the air.
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  8. #7  
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    Quote Originally Posted by SteveF
    Wolfram is the element that we English-speakers call tungsten, symbol W. German speakers call it Wolfram.
    Ahh I see.
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