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Would this experiment lights the bulb for a moment?

  1. Jul 1, 2006 #1
    wish to ask, if experiment like below image :
    http://img168.imageshack.us/img168/4417/image28ei.png [Broken]

    would the bulb lights for a "moment or X milisecond?" once we touch the wire B to the bulb?

    assume the wire B is a long long wire (just wire)
    wire A already attached to positive source

    thank you in advance.
    Last edited by a moderator: May 2, 2017
  2. jcsd
  3. Jul 1, 2006 #2
    well, the lightbulb is always emitting light in room temperature, but it's in the infra-red section of the spectrum, if you want the lightbulb to light in visible light you must make it warm enough.

    if you'd put a positively charged object with enough charge on it, it would light the bulb...
  4. Jul 1, 2006 #3
    you mean positively charged object or negatively charged object?
    coz wire A already connected to positive source. :?
  5. Jul 1, 2006 #4
    does it means the "electrons" on the lightbulb, although not connected with wire ~ just the bulb alone) . are always "moving" (maybe in low potential difference), so the lightbulb would somehow emits the "infrared section of spectrum" ?
  6. Jul 1, 2006 #5
    it doesn't matter if the object is charged with a positive charge or a negative one - it's the voltage difference that matters here, not the direction... the current which moves through the lightbulb's wire is only used to heat it up, you dont see light from the current electrons.

    the radiation a lightbulb is emitting is of the king of "black body radiation"
    according to thermodynamics there's a boltzman destribution of energy states amon every "particle" of the system, when a "particle" is above it's ground state, it will eventually emmit a photon and get to a lower state.
    this distribution is dependant upon temperature - you got more excited particles when the temperature is higher.
    in room temperature most of the emitted radiation is infra-red, when you warm it up, to say, 2200 kelvin (about 2500 celsius) you get the usual yellowish light you get from a lightbulb. (and if it's 1000 kelvin it'll be red)
    in a metal wire the "particles" that emmit the visible raidation are electrons, and thats why is put "" on that word - an electron is hardly a particle in the classical sense.

    that's something a little off-topic, but it's a blacl-body radiation example:
    most computer screens comes with two pre-set color schemes, one is 9300K (for brighter white - thats what most people prefer to work with)
    and 5500K (sometimes 6500K) for image management - because our sun is emmiting light like a blackbody radiation with around 5500K-6000K temperature (the surface temperature of the sun).

    when people talk about hues of white, they usually use the Kelvin scale.
    Last edited: Jul 1, 2006
  7. Jul 1, 2006 #6
    thank you for your reply, if possible, could you please clarify the following term. (in plain words) ~ coz i am just a physics beginner.

    you mentioned about positive charged object and negative charged object, could you please explain them a little bit.

    is voltage difference same as potential difference or electric difference?

    you mentioned about "particles", if possible, could you give me a rough idea what it is?

    thanks a lot and i learn something new "black body radiation" :)
  8. Jul 1, 2006 #7
    you're welcom :biggrin:

    a positvely carged object is an object who's total charge is positive (i.e. more protons then electrons for normal life objects)
    and a negatively charged object is an object who's total charge is negative (i.e. more electrons then protons)..

    yes, voltage is electric potential difference - and charge will experience force and thus move (when free) when a a potential difference is introduced, when the voltage increases the force the charge feels increases too.

    when i said "particles" i ment every material microscopic object in general, they all obey the same basic statistics - which say that theres a probability for every object to be in an excited state, and the probability for higher energy states increases as the temperature increases.

    in the case of the bulb, you got electrons and protons as your "particles"
    but the electrons in that wire behave more like waves then anything else.

    to learn more about black-body radiation in laymen's terms try looking at howstuffworks.com or wikipedia.org
    is a good start
    Last edited: Jul 1, 2006
  9. Jul 2, 2006 #8


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    Good work, Fargoth. I just want to backtrack to the original question for a sec. Sleepx2, your diagram does not indicate a closed circuit. Remember that your negative connection has to be to the 'other side' of the positive source. If you hook one wire to the positive terminal of a battery, and the other to the negative terminal of a different battery, nothing will happen. While Fargoth is correct about the bulb radiating IR, it has nothing to do with your electric circuit.
    Pardon the intrusion, but I felt that some clarification was in order. :smile:
  10. Jul 2, 2006 #9
    Thanks, Danger.
    But in his scheme he drew a charged object, and a long wire, for a split second this long wire can be regarder as ground (and after that split second it will charge-up so that there would be no electric field inside the wire), so there would be a pulse of current through the bulb's wire (it's intensity-time shape depends on the charge amount on the charged object, the resistivity of the long wire, and the length of the wire), untill the wire would have a new charge distribution.
    div(j) would be non-zero, because charge builds up in the wire, and not just flow through it...

    so, yes, the bulb can emmit a flash of visible light if the charged body has enough charge.
    i just talked about black body radiation to make it clear that the only part of this pulse of current is heating the bulb's wire up.
    (although in this case, because it's a varying current there could be some photons from the current too, but i don't think they're noticable.)
    Last edited: Jul 2, 2006
  11. Jul 2, 2006 #10


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    Ahhh... gotcha. That's all quite a bit over my head, but it references back to the first thing that I learned about blowing things up. You always lay out your detonator cable before you attach it to the primer cap, because moving it can cause a pulse.
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