1. PF Contest - Win "Conquering the Physics GRE" book! Click Here to Enter
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Ad Hoc Physics discussion & other subjects

  1. Jan 18, 2010 #1
    Can someone tell me how long these computer internet forums have been in action on planet earth?
    When I turn on a light bulb...light waves are produced..are photons "created" or emitted by flowing electrons and if so what causes the electron to do so..or what is the mechanism "inside" the electron that causes it to give birth to a photon?
    Thank you for any and all answers.
  2. jcsd
  3. Jan 18, 2010 #2
    Re: Light bulbs

    Photon creation/emission is a curious thing, especially as you did not specify a type of light bulb.
    Incandescent light bulbs works because of "black" body radiation. The filament is generally made of a thin wire of tungsten. Edison used carbon wires made from thread cooked in an oven. The tungsten has a high melting point. As it is, ideally, in vacuum it won't combust. Because the wire is thin, it has a high current density. With a high current density, there are many electrons imparting energy to the nuclei of the atoms. This nuclei begin to vibrate as a three dimensional simple harmonic oscillator with a frequency distribution equivalent to the temperature. As a nucleus vibrates, it changes the E-field and the B-field. That E-field and B-field disturbance radiates away from the source nucleus as a photon sphere with a frequency of the nucleus. That is what you see with an incandescent light bulb.
    I'll let some one else grab the fluorescent light bulb in similar detail.
    There is nothing inside of an electron, that we know of, that can produce a photon.
  4. Jan 18, 2010 #3
    You said that electrons impart energy to the nuclei of atoms and they begin to vibrate.
    Is this imparted energy a 'collision' energy...or a "momentum transfer energy" between the electron and the nucleus? Does this energy have a name?

    You said that when the nucleus vibrates it alters the e&b field which then results in an electromagnetic wave being emitted. What happens when there is a greater "energy" transfer to the nucleus or a higher vibrational energy? Is a higher energy (shorter wavelenghth) photon emitted?

    Is there a "shortest" possible wavelenght for light? During this activity..could you "destroy" a photon? There's more to that question.

    Is there a "longest" possible wavelenghth for light? If you reached a lowest energy limit...and just a hair below that..could you alter the 'velocity' of light?

    Thank you for any and further responses.
  5. Jan 19, 2010 #4
    They are already vibrating, just generally not in the visible range.

    "Momentum transfer energy" would be good way to describe it. I would call it kinetic energy when the electron has it and thermal energy when the nucleus has it.

    The amount of energy transfer has a probability distribution, I would guess either a Gaussian/normal distribution or black body distribution. Higher energy transfers happen, but so do lower energy transfers. A higher energy transfer results in more thermal energy in that nucleus and so, yes, a higher energy photon is emitted.

    I have given those questions about shortest and longest possible wavelength a thought before. I have not come to a satisfactory answer in either case. I doubt any one else has either.

    One can not destroy a photon by making it's wavelength shorter than the minimum wavelength, if a limit existed. I think it would split itself into two or more photons of equal energy, similarly to the decaying subatomic particle.

    I'm assuming you're not interested in refractive index and it's origins. People are already slowing photons down in quantum mechanical devices as in superfluids. Dr. Lene Vestergaard Hau brought light to a stop in a superfluid of sodium. That stop would be better stated as capturing the information of the light and then retrieving that information at a later time.
  6. Jan 19, 2010 #5

    Claude Bile

    User Avatar
    Science Advisor

    Re: Light bulbs

    No; the energy is imparted to the 3D network of bonds that bind the solid together, hence whole atoms (nucleii + valence electrons) vibrate, not just nucleii.

    Sure there is! EM waves are emitted by oscillating charges, since electrons possess charge, they can potentially emit EM radiation.

  7. Jan 19, 2010 #6
    Re: Light bulbs

    The approximation is the nuclei because it has the mass. I've also heard from my profs. the ion instead of the nucleus which would include non-valence electrons. The ion would be a better approximation because you are considering all that could be vibrating. Valence electrons in a metal crystal lattice are not associated with any ion.

    There IS NOTHING IN an electron. The fact that electrons ARE charges allows them to potentially produce EM waves. That is not the mechanism at work.
  8. Jan 20, 2010 #7
    I need the questions at the bottom answered so I can continue the conversation.
    The one's about the shortest and longest possible wavelenghth...actually..for conversational purposes I should have said "amplitude".

    Thanks for you further response.
  9. Jan 20, 2010 #8
    I know there is no mathematical upper limit on the magnitude of an EM wave, simply add more photons. The upper limit would be due to the physical nature of the universe and the fact you could not convert all of the universe into light and have be anything meaningful or useful.
    Photons are funky things. You can talk about them in terms of particle quanta and in terms of continuous probability waves. The minimum amplitude of an EM wave is equal to one photon. What that number would be in either N/(Am) or N/C (E and B fields), I have no idea.
  10. Jan 21, 2010 #9
    Sorry about the haphazard (or time stretched) nature of this discussion..but hopefully something useful will come from it.

    I have also learned recently that emailing and posting etiquette in forums like this should have the requirement that the first line begin with a friendly greeting like the word hello..otherwise the speaker seems like he is complaining or charging the receipient with being less than smart or being unduly wrong about something.

    There is also a point to my questions..but I am not going to reveal it at this time.

    For argument sake I will assume that a GammaRay photon is a 'wave' and it has a (high) frequency (that was the word) I was looking for in the past. My guess or question is what is the energy level (or frequency) of a gammaray photon in scientific notation? and could you increase the frequency or energy level ..so much..that you could "squeeze" the photon to death or 'right out of existence'? and if not...why not? or what happens?

    At the other end..the lowest frequency (or stetched) light wave is the radio photon..what is the "lowest" energy level (or frequency) of a radio photon? If you "went below" this energy level..what happens? Does the "machine?" not produce a radio wave at all? Can you remind me what this "machine" is....its the machine I am most interested in! What gives birth to photons in the Universe..or what is the mechanism that causes in creation from (electrons?)
    ..sorry about that reference..but maybe you can correct me?

    Thanks for any and all answers.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Physics discussion subjects Date
I Understanding Bernoulli's Principle Yesterday at 1:28 PM
I What physics does this BVP represent? Thursday at 2:04 PM
I MRI physics question Tuesday at 6:23 AM
I Physics term for discussed example and calculations Sep 23, 2017
Physics HW FAQ Discussion Apr 17, 2005