Wavelength vs. amplitude

  1. bobie

    bobie 682
    Gold Member

    Is there a relation between the wavelength and the amplitude of a photon (or particle), or all frequencies have the same amplitude?
    If the latter, why the wavelength affects the way a radiation passes through matter or slits?

    Thanks.
     
  2. jcsd
  3. PhysicoRaj

    PhysicoRaj 437
    Gold Member

    There is no dependance of amplitude on wavelength. And it is not necessary that all frequencies (equivalently wavelengths) must have same amplitudes.
     
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  4. bobie

    bobie 682
    Gold Member

    Can you answer the second question, too?
     
  5. Larry Gopnik

    Larry Gopnik 10
    Gold Member

    Indeed, Amplitude is not affected, it is merely a 'loudness' I do believe. (Or so I was taught at about 13, therefore it may be wrong).

    As for depending on diffraction, longer wavelengths equal lower frequency. That means the wave has less energy, and therefore diffracts more. This is as it is more deeply effected by its environment. That's why wavelength affects awes going through slits more.
     
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  6. bobie

    bobie 682
    Gold Member

     
  7. PhysicoRaj

    PhysicoRaj 437
    Gold Member

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  8. PhysicoRaj

    PhysicoRaj 437
    Gold Member

    That I think is rather a misconception. The wavelength must be comparable to the slit width to get an effective diffraction.
    See these in the wiki:
    http://upload.wikimedia.org/wikipedia/commons/thumb/4/46/Wavelength%3Dslitwidthspectrum.gif/220px-Wavelength%3Dslitwidthspectrum.gif

    http://upload.wikimedia.org/wikipedia/commons/thumb/0/0a/5wavelength%3Dslitwidthsprectrum.gif/220px-5wavelength%3Dslitwidthsprectrum.gif
     
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  9. Nugatory

    Staff: Mentor

    Save yourself some grief and try to forget that you ever heard the word "photon" - you can rediscover it when you get to quantum electrodynamics.

    Here you are describing a purely classical wave problem, and even thinking in terms of photons is pretty much guaranteed to confuse you if you can't describe and analyze it in classical terms.
     
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  10. bobie

    bobie 682
    Gold Member

    Do your remark apply also to an electron passing through a slit or a hole?
    Also, is there any clue to the amplitude of visible light wave?, or of an electron travelling say, at 10^7 cm/s ?
     
  11. Larry Gopnik

    Larry Gopnik 10
    Gold Member

  12. bobie

    bobie 682
    Gold Member

  13. sophiecentaur

    sophiecentaur 13,541
    Science Advisor
    Gold Member

    Amplitude of a 'light wave' (or any other EM wave) is a function of the total number of photons involved and not the energy in an individual photon.

    Re your comments about electrons, you would hardly expect to get 'big or small' electrons, would you? So amplitude of an electron beam would have to refer to the number of them or the total energy.

    Do not reject Nugatory's remark about photons. If you want to discuss wave phenomena then forget the particular nature of Photons or Electrons. You cannot have both views at the same time.
     
  14. sophiecentaur

    sophiecentaur 13,541
    Science Advisor
    Gold Member

    I sometimes wonder whether you actually read anything other than what people write on PF. Wiki and Hyperphysics are full of stuff about diffraction and interference. You can find such a lot of information about the basics of the diffraction of waves. I'm afraid it's very Maths based, but that goes with the territory and it does involve some effort on the part of the reader.
     
  15. bobie

    bobie 682
    Gold Member

    What if the number of photons involved is 1?
    I was referring to one single EMR light-wave or electron: if light is a wave, can there be a wave (of any kind, EM sound etc) without amplitude? I supposed not.
    Probably I was wrong, but if a light wave must have an amplitude, I'm asking: what is it and, is it related to frequency?

    2) I was told in another thread that now you have electron pumps that can shoot single electrons. Or, imagine an individual electron shot in a cathotic tube, I supposed both go straight like a bullet, else, we could never move it around with precision and get a TV-picture. Am I right so far?
    Now imagine that, knowing the precise trajectory of the electron we put exacly in its path a screen (I said wooden to avoid magnetic or other interference) with a hole of varying diameter. There is certainly a point where it would pass throug the hole.
    I do not know if this experiment can be made in practice or if it is just theoretical, my question is:
    (whatever the real nature or size , if it is poinlike or a wave, or both) how big must the hole be for the particle to go through? and, would it vary with the speed of the electron?

    Thanks for your help
     
    Last edited: Mar 10, 2014
  16. PhysicoRaj

    PhysicoRaj 437
    Gold Member

    A photon is not a wave again. The wave is not a photon. They are both two ways of interpreting the same thing. The intensity of light in the wave sense refers to it's amplitude. In the particle sense it refers to the number of photons.
     
  17. PhysicoRaj

    PhysicoRaj 437
    Gold Member

    Are you saying that the width has something to do with amplitude?
     
  18. Drakkith

    Staff: Mentor

    Classically, the amplitude of an EM wave is a measure of the strength of the electric and magnetic fields. You can imagine this as the amount of voltage and current induced in an antenna that detects the EM wave. A higher amplitude EM wave will cause more voltage and current in the antenna than a lower amplitude EM wave. Amplitude is not related to frequency.

    The uncertainty in the position of an electron is very small. Many orders of magnitude smaller than the size of a single pixel on a CRT. So while we don't actually know the exact position of the electron, it turns out we don't need to.

    No matter how small you make the hole the electron will always have at least a small probability of passing through. This even applies when there is no hole, since the electron can tunnel through a solid barrier and appear on the other side. The thicker the barrier, the smaller the chance is.
     
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  19. bobie

    bobie 682
    Gold Member

    Thanks, drakkith, did you mean small, or big?
    is the material of the barrier relevant?
    does conductive material make any difference?
    What I am really trying to understand is on what exactly probability is dependent:
    suppose we could reach such a precision in adjusting the pump and that we succeed in getting an electron through a hole of, say, 1mm, if we keep shooting do all electrons pass through the hole?

    One last question, in water we can concretely measure the amplitude of a wave, is there a physical amplitude in sound waves and light waves, too?
     
  20. PhysicoRaj

    PhysicoRaj 437
    Gold Member

    He meant small. The material does count on the electron being able to tunnel through.

    It really depends on a lot of factors. See this:http://en.wikipedia.org/wiki/Quantum_tunnelling

    Yes in the case of sound wave. Amplitude in case of light is basically the maximum value of electric and magnetic fields.
     
  21. bobie

    bobie 682
    Gold Member

    I was not referring to quantum effects but to macroscopic world.
    it is more probable that the electron passes through a hole with r= 1 cm or 1 mm?
    and through a hole in wood or iron?
     
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