Different wavelenghts one photon.

  1. I apologize as this question would be answered probably by a google search but as a simple question maybe it would have some interest from others too.

    So How do we have different wavelength of visible light different frequencies of AC the mains 50hz and upto khz in the smps and even more on radio waves and tv broadcast.
    Well ok I understand why is the frequency like 50hz in the "mains" as with the generator rotor speed and so on but all these fields are electromagnetic fields and the carrier in all the cases is the massless photon.And because the photon is massless it can reach "c" and always travels at c so when it has a fixed speed and constant speed all the time why do the field it mediates can have so varying spectrum of different frequencies?
  2. jcsd
  3. sophiecentaur

    sophiecentaur 14,715
    Science Advisor
    Gold Member

    You need to be very careful when you start talking about photons. Electromagnetic radiation can be treated nearly always as a wave phenomenon. Waves are pretty straightforward because the same concepts apply, in most respects, to EM, sound and ripples on water. Waves all have a speed, wavelength and frequency and the wavelength of em waves can be anything from thousands of kilometres (Mains electricity) to a small fraction of the size of an atom (gamma rays) - just like sound waves but with a much bigger range. Visible light is just a small portion of the whole range. Why should it not have a range of frequencies?

    Don't be lulled into feeling that you can also treat photons like little bullets. They are nothing like that. I, personally, think it's a shame that the word 'particle' is used because of all the baggage it brings with it.
    Until you learn a lot more about the nature of photons, the only thing you can be sure of is that they are a quantum of energy and that EM energy comes in quanta with a value dependent on the frequency of the em wave.

    P.S. A google search would be a good idea.
  4. HallsofIvy

    HallsofIvy 41,264
    Staff Emeritus
    Science Advisor

    I am a bit concerned about you reference to "different frequencies of AC the mains 50hz and upto khz in the smps". You understand that the motion of electrons in electrical wires has nothing to do with "photons", don't you?
  5. Yes indeed I understand that the motion of electrons and the mains frequency or any other frequency has nothing to do with photons directly but the field that these moving electrons create is the EM field and physics says it is mediated by the massless photon thats why this question arose.
    Ok don't go hard on this one but it looks like a field mediated by a "particle"or whatever would I better call it that has actually nothing much to do with the characteristic of the field itself or how it behaves?
  6. Hmm could I say that the electrons in wire creating the em field that is mediated by photons is something like a baseball game where the electrons are the players and the photons are the ball and the communication happens when the ball is being hit by the bat , ofcourse in the field the ball is traveling at c.
    So there are alot of electrons (players) and even more photons(balls) in a em field of any frequency.
    Is that close to reality or totally off?
  7. sophiecentaur

    sophiecentaur 14,715
    Science Advisor
    Gold Member

    That's a metaphor which I can't imagine is very helpful. Why not go for a model that's well established. As I wrote earlier, initial thoughts about em are more likely to be useful if they are based on waves and fields.

    Do you have a proper idea about what you mean by the word "mediated", in this context? What is your level of knowledge of this subject? It isn't clear. from what you have written.
  8. Well as I understand it when voltage is applied to a conductor electrons "join hands" and start to flow through the wire that movement causes some interaction with the surrounding medium consisting of atoms and something happens ,,and this exact place I'll leave up to you to describe more properly,,
    so when the electrons start to move an em field is created and I guess it's like throwing a rock into a still water surface the wave is created in each direction from the point of contact.
    Only in water the traveling wave is the water itself but in EM field the traveling wave is doing that via photons, and the higher the frequency the higher the photon energy.
    Well that's how I understand it.
    Could I say the the photons are the force carriers of the EM field just like gluons are for the strong nuclear force?
    And a question about dc does it create and em field that consists of photons? Because photons must have a certain frequency but the dc field is stationary as long as i recall correctly?

    By the way if i set up a simple transmitter through somewhere in space through which I just send a simple 1mhz sine wave according to the fact that em wave travels at c in vacuum , I should be able to pick up that signal anywhere in space ? Ofcourse all the radiation from stars and all other background "noise" would probably affect the signal badly I guess.
    Last edited: Nov 29, 2012
  9. sophiecentaur

    sophiecentaur 14,715
    Science Advisor
    Gold Member

    You could say that, perhaps, if you wanted to describe what happens when the field in an em wave interacts with a charge but I thought that describing photons as mediating particles was in the interaction of two charges, rather than in the context of an em wave. The photons in a Feynman diagram are virtual photons afaik and are exchanged rather than just arriving and causing a change in energy for a charge system.

    I keep getting the feeling that you have a few terms buzzing around in your head and have not yet read / learned enough to join them up in a meaningful way. You appear to be trying to build up a very personal picture of this topic. I seriously suggest that you should try to increase your knowledge of this by reading rather than by asking somewhat random, self-generated questions.

    The whole thing is described at a whole range of levels and I'm sure you can find something on the Web that suits your level and that can take you forward, usefully. Once you actually know more, things will become clearer for you. At the very least, it will enable you to ask more 'answerable' questions. :smile:
  10. Nothing is totally random rather just a specific outcome of many possible ones just like with my questions.:)
    But was my question about the dc case and the transmitter in space so way off or was it just that you didn't considered them to be related to my original question?

    Yes I have to learn and I am doing that we all do but only I do it in the way that I can do it the best in if i get some questions from that way I come here.
  11. sophiecentaur

    sophiecentaur 14,715
    Science Advisor
    Gold Member

    A field does not 'consist of photons'. Photons are only involved when there is some change so the dc issue does not apply. You must learn more about these things before it is worth asking that sort of question. Your questions cannot elicit useful answers as they stand.
    As for the transmitter question, once an em wave has been emitted, it carries on going for ever (until it's intercepted) if the source is a point (or small enough) the power flux through a given 'window' will drop of according to the inverse square law.

    I could compare the way you appear to want to find about about this subject to someone in a maze who has access to a map but would prefer finding the exit by blundering from passage to passage on the offchance of finding a way out. That approach is just not effective use of time or resources (PF etc.). Try to restrict a post to just one question, for a start.
    What have you been reading, so far?
  12. Well I have been reading QED and other stuff but the main problem is that I will try to get on a real physics book than just articles from the internet.The information is the same but in internet is much harder to sort out the good needy things.
    Also i have been checking alot of PF threads with the information that interests me and all the links in them.

    Well thanks for answering those two questions.Even though I had an close idea that dc has a static field just wanted to make sure.
  13. sophiecentaur

    sophiecentaur 14,715
    Science Advisor
    Gold Member

    I'm sure that will help. Also, the Hyperphysics pages are pretty good for most subjects - they tend to present things in a good order. I think part of your prob is that you've jumped in half way through. :smile:
  14. Yes hyperphysics has some good stuff in terms of explanation.
Know someone interested in this topic? Share this thead via email, Google+, Twitter, or Facebook

Have something to add?