Which bulb lights up first?

Discussion in 'General Electronics Chat' started by RamaD, Jan 9, 2012.

  1. RamaD

    Thread Starter Senior Member

    Dec 4, 2009
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    Three bulbs are connected in series, and, a DC voltage is applied. Which bulb lights up first? Electrons move from -ve to positive, and, at speed of light, about a foot per ns.
    Simple question posed to me.
     
  2. Lundwall_Paul

    Active Member

    Oct 18, 2011
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    Are they CFL bulbs in cold weather? If they are none will light.
     
  3. kubeek

    Expert

    Sep 20, 2005
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    A fraction of a ns will the ones closer to -ve "light up faster" or actually notice the current faster. If you take into account how long it takes for the filament to heat up, they start glowing at the same time.
     
  4. KMoffett

    AAC Fanatic!

    Dec 19, 2007
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    Actually the "effect" of electron movement is near the speed of light, but the electron movement is much slower. Since all of the electrons essentially move together along the series circuit, like boxcars on a train, all of the bulb filaments are exposed to the movement of electrons at the same time.
    http://amasci.com/miscon/speed.html

    Ken
     
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  5. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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  6. BillB3857

    AAC Fanatic!

    Feb 28, 2009
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  7. PaulEE

    Member

    Dec 23, 2011
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    I second that answer. I believe I saw this in an MIT opencourseware lecture video on circuits.
     
  8. w2aew

    Active Member

    Jan 3, 2012
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    ...so the answer is - the bulb that has the highest cold filament resistance will likely light up first - because it will begin to dissipate the most power first, thus increasing the filament resistance more, thus beginning to starve the others of current. Of course, this assumes that all the filaments have the same thermal time constants, etc...
     
  9. kubeek

    Expert

    Sep 20, 2005
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    They are in series, so the hotter one starves others of voltage.
     
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