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Planck's quantum theory question

  1. Jul 22, 2011 #1
    electromagnetic energy is quantized (it only comes in discrete units related to the wave function)....

    my exam krackers book says: "if we transfer energy from one point to another via an electromagnetic wave, and we wish to increase the amount of energy that we are transferring without changing the frequency, we can only change the energy in discrete increments given by:
    [itex]\Delta[/itex]E = hf

    my question is:

    Based on the equation, how can you increase the amount of energy that you are transferring without changing f (since h is a constant)?

    does increasing the amount of energy this way mean using more photons?
  2. jcsd
  3. Jul 22, 2011 #2


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    Yes! The only way to increase the energy transferred without changing the wavelength is by increasing the amount of photons released and absorbed!
  4. Jul 23, 2011 #3
    Regarding Drakkith's answer! This is my first time on the forum so I hope I'm following protocol.
    Drakkith, does this mean more atoms have to be involved, for instance by increasing the current in a transmitting antenna? It appears to be a problem of density...is that correct?
  5. Jul 23, 2011 #4
    E = hf is a continuous wave formulation..

    it does not address individual photons...you can increase power by adding one more photon..

    you can visualize the discrete nature of EM waves this way:


    So for example, when a bound electron emits or absorbs a quanta of energy...of electromagnetic radiation...it is not a continuous phenomena.

    ",,,the current in a transmitting antenna? "

    increasing the current means increasing the flow of electrons....not atoms....

    One way to look at antenna power is via the Poynting vector: S = 1/u0 E x B

    so anything that increases the amplitude of E or B increases the transmitted power. You can increase received power by antenna focus...directivity
  6. Jul 23, 2011 #5
    I was under the impression that all photon energy was now accepted as being discrete packages of energy in nature, how can it be continuous. I thought based on Planck's work that Einstein saw iphotons as packages of energy, not continuous.
    Isn't that what Planck had determined in order to explain black body radiation behavior?
    Anyway, I meant that if you pass a current through a wire and it emits electromagnetic energy, such as a radio antenna, then the only way you can get more electrons involved, as you correctly pointed out, is to have more atoms involved. Are there free electrons for instance in a copper wire that are not associated in atomic orbits? What is the method used to increase photons to answer Gkangelexa's question?
    Last edited: Jul 23, 2011
  7. Jul 23, 2011 #6


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    It is a packet of energy. The amount of energy that can be in that package is continuous though. And black body radiation has more to do with the limited number of electrons and atomic orbitals than with the actual photons themselves.
  8. Jul 23, 2011 #7
    Ok, I accept that the energy in a photon is continous, it has no gaps for the duration of the photon passing a point in space. Now, if I may I would like to get back to Gangkelexa's original question, of how to increase the energy without increasing frequency? I asked you at that point if it was a matter of density, by that I meant getting more atoms involved to produce more photons? Is that correct? If you can't increase the frequency output of the emitting atom, then you must need more atoms to emit photons of the same frequency, is that correct?
    Last edited: Jul 23, 2011
  9. Jul 23, 2011 #8


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    Yes, you need to emit more photons, through some means, to increase the energy.
  10. Jul 23, 2011 #9
    Thank you Drakkith for both your help and your patience.
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