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Do all photons have=energy

  1. May 17, 2005 #1
    This maybe a dum question! Does the wave length/frequency of a photon decide its energy level? If so, does this mean the energy of all photons, in fact, is equal because actually its energy is spread out of a larger space and seems different? This would mean that a high frequency shorter wave length photons would be more compact and appear to be higher energy while lower frenquency longer wave length photons would appear to have lower energy levels.
  2. jcsd
  3. May 17, 2005 #2


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    Gamma rays have a frequency of 10^22 Hz and a wavelength of 10^-14m

    They are the most energetic form of light with the highest frequency, conversly the shortest wavelength...

    A higher frequency wave is carrying more energy. If you increase the intensity you are only increasing the amount of photons - if you increase the frequency than you are increasing the energy. Waves on the right of the electromagnetic spectrum carry more energy than that of visible light or radio waves.

    However all forms of light travel at 3.0*10^8 m^-1.

    What is really meant by energy = light ??? Hmmmm i don't really know.
    I would prefer to look upon energy as the most fundamental entity - that which is opposite to space - so matter = energy and this energy will take the form of different bodies - i.e mass....

    Im still trying to figure out this line of thought. They say that photons have no mass - so therefore they would / should not exist. They must have mass - even if it is a minute amount, otherwise how do they come into interact with gravity. Mass is a function of density * volume so the photon does physically exist therefore it should be classified with a mass. However this comes into contradiction with the whole mass/energy scenario.

    Why do they travel at 300,000Km/Sec - this is an absolute velocity. Photons don't adhear to energy application - in other words if you increase the energy of a photon its speed will not change. Maybe this is converse to the latter section of the law of intertia - '' a body placed sufficiently far from other bodies (meaning no interaction of any kind) will either be at rest of move at uniform velcotity and direction (motion) in a straight line''???

    The photon moves at a uniform velocity and motion because of its almost massless-like state???? I don't really know.....?


    On another topic - has anyone heard about the creation of the EM field after the proton is created by way of beta - decay.
    Last edited: May 17, 2005
  4. May 18, 2005 #3
    try to get it

    Interesting that energy should be so indefineable... I don't think you answered my question. Let's say that energy is what's being communicated by light and stored in matter. If we looked at waves on the macro level the bigger the wave - longer the wave length and lower the frequency - the more power it has because it is moving more water/matter/medium with it. So we know that photons at the quantum level are the opposite. Whatever energy is it seems compressed in small photons (i know that photons aren't supposed have space but descriptions like wave length and frequency certainly imply a spatial dimension to them) so they have a bigger affect when they hit things while the larger they are the smaller the affect they have when they hit things. Are we saying that all photons are the same size and the energy changes according to the wave length so that there are many more photons communicating energy in a long wave length low frequency radio waves than in a short wave length high frequency gamma rays.
  5. May 18, 2005 #4
    sorry meant "trying to get it" not "try to get it"
  6. May 18, 2005 #5
    Wrong. Type "planck's constant * 10^22 Hz in GeV"

    into google, and you'll see that these are only 41 MeV.

    Particle accelerators produce much higher energy photons all the time.

    I don't think there's a theoretical limit to the energy of a photon, but if there is one, it may be dictated by the Planck time, and on the order of 10^19 GeV, according to the uncertainty principle.
  7. May 18, 2005 #6
    E = h * frequency of photon = h * c / wavelength of photon

    where h is Planck's constant, and c is the speed of light.

    So, by this equation, no the energy is not constant as a function of either frequency or wavelength.
  8. May 18, 2005 #7
    thanx for pointing me direction to look... i looked up Planck and compton and co. Still not really satisfied... The problem maybe that I'm thinking of photons in terms of size because it seems to affect the systems we have for receiving or if you like measuring the affects of photons, in fact measuring the photons themselves, defining the energy levels. Does a change in energy level of a photon change the frequency and wave length? Once the frenqency and wave length reach a threshold of tininess ;-) does the momentum transform into mass at some point???
  9. May 18, 2005 #8
    your questions is quite bizzard, you are asking if the more energetic photons are accualy smaller, then they may have one and the same energy but packed in a little space, there may be reason in this

    from classical physics it is known that bigger oscilating bodies produce waves bith bigger wavelenght, this means that the wavelenght depends from the size of the vibrating object, there is connection between 'size' and 'frequency'.

    if you look at physics the 'smaller' objects produce waves with bigger energy, atom specters are more energetic then molecular, nuclear are more energetic then atomic and so on. The size of the oscilator determines the maximal frequency of its radiation
  10. May 18, 2005 #9
    You a good point about the way more concentrated energy photons are produced but I don't know if that's proves my point wrong xgen. It just confirms the idea that if we measured energy in a more abstract way photons could have the same amount of energy jsut focussed in different ways by the wave length/frequency say by the aggregate effect caused by the momentum of the particles. High energy particles with its energy concentrated into a minute fraction of a meter move neutrons from the nucleus which means breaking through the strong force while a photons with its energy spread over several meters needs a delicately balanced electron in a molecular matrix that is almost free floating to be noticed. what would happen if we could do nothing other than change the wave length/frenquency of the photon.
  11. May 18, 2005 #10
    I'm sorry - but this is barely one step removed from a completely random assortment of physics words strung together. That's why it's important for physicists to use equations within a theoretical frameowork to give their words meaning.
  12. May 18, 2005 #11


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    I agree. Besides ...
    This is wrong. Classically, the power increases with the amplitude, which you seem to be confusing with wavelength.

    I suggest geting classical (actually, the practice of working with well defined quantities and relationships instead of unstructured ideas and connections) concepts clear before venturing into quantum mechanics.
  13. May 19, 2005 #12
    Here's an interesting thread from sci.physics.research.


    Scroll down to the "length of a wavetrain of a single
    photon" thread. There's lots of great stuff on photons
    in the sci.physics.research archives. Try sci.optics also.
    The best thing to do of course is to get a book on
    the quantum theory of light. Any book will tell you
    the prerequisites for understanding its contents.

    There are relatively few people in the world who
    actually understand this stuff. Perhaps one day you
    and I will join that group. :)
    Last edited: May 19, 2005
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