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Waves & wavelengths

  1. Jun 6, 2010 #1
    Are waves only 'waves' if you try and represent them in 2D? If an object emits waves in all directions are the waves more like expanding spheres?

    If a wave/sphere hits us and the source is sufficiently far away (and strong?) do we 'experience' it as though being hit by a plane? or multiple repeating planes, where the planes are more dense in the wave peaks and lesser in the troughs?

    Does wavelength refer to how narrow the distance between peaks & troughs are and is there a separate description for signal strength? Does it spread out like light photons do, over distance? (have I just described the same thing?)

    What about more directional emitters, would they be the same, only the planes are more local as it where?

    Can/do multiple waves of different wavelengths be hitting us at the same time? Is this because they can share the same quantum state?

    Given a sphere of #unlimited light sources shining inwards into a limited space, is there a limit to how many photons can occupy the same physical location?

    Are wavelength and speed independant? 20 questions, apologies feeling really enthusiastic.
     
  2. jcsd
  3. Jun 6, 2010 #2
    Forgive my self-indulgent lack of proper vocabulary. Also my questions are a bit 101 and by #unlimited I should probably say infinite. Thanks in advance to anyone who has time.

    Do all parts of the colour spectrum (from the same source) move at speed c?
    Are all parts of the colour spectrum photons?
    Can photons from the same light source ever occupy the same space?
    If light is reflected does that change the source?
    Does anyone know if there is any part of the universe that hasn't received light at some point, or isn't currently receiving light? Does anyone know what/if any parts of space contain a record minimum/maximum lumens?
     
  4. Jun 6, 2010 #3
    If all parts of the colour spectrum move at speed c are the wavelengths of the very first outgoing light in sync/lined up?
     
  5. Jun 6, 2010 #4
    Hi,
    All electromagnetic waves travel with speed of light (includes color spectrum).
    [tex]c=\lambda f[/tex].c is constant.
    Yes all are photons.
    i dont understand your 3 and 4th question.
     
  6. Jun 6, 2010 #5
    Electromagnetic radiation propagates at c. Visible spectrum is just part of em spectrum.

    Photon is smallest quanta of em radiation energy for given frequency. So, yes whole spectrum is quantized. Energy of a photon is given with E=hV. Radiated energy must be some integer value multiplied with energy of single photon.

    Yes.

    No, unless it is reflected towards source, and hits it again.


    Globally, it is all the same. Our universe is homogeneous and isotropic.
     
  7. Jun 6, 2010 #6
    Are waves only 'waves' if you try and represent them in 2D?

    you have to define what you mean by a wave..in two dimensions waves appear as curved lines...

    If an object emits waves in all directions are the waves more like expanding spheres?

    yes now you are taking 3D.

    If a wave/sphere hits us and the source is sufficiently far away (and strong?) do we 'experience' it as though being hit by a plane?

    yes, approximately if the source is a point source....

    or multiple repeating planes, where the planes are more dense in the wave peaks and lesser in the troughs?

    electromagnetic waves have unfirom density...not water waves....

    Does wavelength refer to how narrow the distance between peaks & troughs are and is there a separate description for signal strength?

    yes,yes..signal strength might be represented by height of peaks and troughs....but "signal strength" is a separate conecpt...you can read in information theory....

    Does it spread out like light photons do, over distance? (have I just described the same thing?)

    Photons don't spread out, waves do....photons are quantizied (pieces) of waves.....

    What about more directional emitters, would they be the same, only the planes are more local as it where?

    Directional emitters are focused...think of a wave generator in a lab where the sides are constraining and the waves move in one direction from the flat source....

    Can/do multiple waves of different wavelengths be hitting us at the same time?

    happens all the time

    Is this because they can share the same quantum state?

    no. it's because there are multiple sources.

    Given a sphere of #unlimited light sources shining inwards into a limited space, is there a limit to how many photons can occupy the same physical location?

    Am unsure..Pauli exclusion applies to fermions..matter particles....and limits THEM ...photons are different, no matter/mass and I do not know exactly what quantum mechanics says...

    I suspect there is no limit....think about six flashlights shining on the same point....six different electromagnetic waves impinge..there does not seem to be a limit....

    Are wavelength and speed independant? 20 questions, apologies feeling really enthusiastic.

    yes for electromagnetic waves, speed is constant c; not so for water waves for example where there is a formula relating them...
    http://en.wikipedia.org/wiki/Dispersion_(water_waves [Broken])
     
    Last edited by a moderator: May 4, 2017
  8. Jun 6, 2010 #7
    Do you mean visible or electromagnetic radiation in general? Might be a different answer...

    During early cosmological inflation, associated with the big bang, there was no light anywhere....no EM could get through all the charged particles....after that, cosmic microwave background radiation made it thru...what we observe now much cooled and red shifted....

    record max, min??
    max
    I'd look near the surface of a black hole where all light is gravitionally curved so that an observer sees a concentrated light radially above....but my guess would be in the vicinity of a supernova explosion:
    http://en.wikipedia.org/wiki/Supernova

    min now....hmmmmm???? if visible light, inside any planet; if EM, maybe inside a huge deposit of lead somewhere???
     
    Last edited: Jun 6, 2010
  9. Jun 6, 2010 #8
    Thanks for all the answers - I'm still reading.
    I'd like to also ask is the energy of a photon a constant? Is this Plancks constant? Are all photons equal?
    and what is wavelength if not the density of photons? Is it the density of something else?
     
  10. Jun 6, 2010 #9
    No offense intended. I'd like to offer some advice to learn these concepts more effectively. This method of asking a bunch of questions and getting quick answers does not seem effective, and this is clearly revealed by these last questions you ask. It would be better to track down a physics book (at the appropriate level for you) and learn the basic fundamentals from square one. A one-on-one tutor/teacher is also more effective than us trying to convey all the relevant concepts over the internet. However, at the appropriate points, some very focused question posted at PF can really help you break through any conceptual roadblocks.

    You are basically taking on the understanding of waves, plus the whole issue of the wave particle duality of light, all at once, and without the proper structure for learning. These are not trivial concepts even when taken one by one with the proper textbook and teacher.

    I first learned the basics of waves from the following book. If you are at an early college level for math, I'd recommend this. If you are not at this point yet, there are other less mathematical books that can get the concepts across just as effectively.

    https://www.amazon.com/Vibrations-W...=sr_1_3?ie=UTF8&s=books&qid=1275837215&sr=8-3

    Once you understand the main fundamentals of waves given here (not the entire book), you can look at the quantum properties of light and the wave/particle duality principle.
     
    Last edited by a moderator: May 4, 2017
  11. Jun 6, 2010 #10
    Thank you for sharing, and your time. I hope my continuing method of asking a bunch of questions and getting quick answers doesn't upset you. I appreciate your advice very much and the book reference.

    You have in fact presaged my next post: Can anyone recommend good books other than Brief History of Time? I have just finished this book and enjoyed it so much it is responsible for all my questions and enthusiasm - actually just as responsible is the generosity here (given that I am an enthusiastic amateur with basic maths who niether works in nor studies in the field) and web pages I continue to find and read.

    I hope my posts don't come across as litter or spam.
     
    Last edited: Jun 6, 2010
  12. Jun 6, 2010 #11
    Ah, got it: c = wavelength.frequency. Still reading, Thanks
     
  13. Jun 6, 2010 #12
    It's not upsetting at all. :approve: On the contrary, it's good to see your enthusiasm, and it is very commendable that you want to learn. I've just been through this process many times as I learn new things. You eventually learn the most efficient process to get the fundamentals down, and then incrementally work through the various conceptual sticking points by talking to others that have already been through the process.
     
  14. Jun 6, 2010 #13
    Energy of a photon is relative to the observer. You can't specify 'absolute' energy of a photon. There is, of course, special case when emitter is at rest in observers inertial frame, but that does not make photon energy absolute in any way.

    If you by 'constant energy' mean constant relative to the observers which are all at rest with respect to each other, then yes.

    I think that you should scout the web for wave/particle duality, photoelectric effect and double slit experiment.

    Edit: Steven is right. You should follow some text book, and ask specific questions about things you are having trouble with.
     
  15. Jun 6, 2010 #14
    Thanks, I will probably do that. I was scouring the web for black body radiation and got as far as the oven with a hole experiments. I understood the equality of emittance and absorption, but quite what is happening inside glass, metal and soot at the atomic/subatomic(?) level in each case will probably require further reading. Also the maths that leads to the quantization of energy absorption/emittance (have I got that right?) I must take on faith.
    I shall also scout the web for your suggested next bits :)
    Thx
     
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