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What do they mean that energy is quantized?

  1. Aug 24, 2013 #1
    What do they mean that energy is "quantized"?

    I am SICK of hearing that "energy comes in packets". I understand what they are saying, but I don't comprehend it, or understand the intuition behind it. Someone PLEASE clear this up for me. Obviously, I speak English, and I understand the words, but I don't comprehend the deep meaning or even the context to which this statement it applies to.

    Do they mean "energy come in packets" when light is absorbed by the electrons, or when the electrons give off energy after being hit by light? And WHY does energy come in packets? WTF, it doesn't make any sense. You can tell me you milked a dinosaur, but it makes absolutely no sense. SOMEONE CLEAR THIS UP!! THANK YOU IN ADVANCE!!
  2. jcsd
  3. Aug 24, 2013 #2


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    When electromagnetic waves interact with matter, regardless of whether it is during emission or absorption, they transfer their energy in "packets". The amount of energy in each packet is determined by the wavelength of the light, with smaller wavelengths having more energy per packet than longer wavelengths. Once you get into the UV range and above, the amount of energy per packet is so high that it can knock electrons out of their orbitals when the energy is absorbed. That is what they mean when they say energy is quantized.
  4. Aug 24, 2013 #3
    More usually one would say that (electromagnetic) energy comes in the form of particles (known as photons). Each photon carries a certain amount of energy.

    Once you see radiation as particle-like, much of the difficulty is removed as this quantization is the expected behaviour of sub-atomic particles (for example, just as an atom always has an integral number of electrons, so it always absorbs an integral number [usually 1] of photons).
  5. Aug 25, 2013 #4


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    Are you familiar with the photoelectric effect? This is what Einstein won the Nobel prize for. Basically, in a metal, electrons are bound to the metal with a fairly weak bond. If the bond didn't exist then they would simply fly off without any "push", but they do need some energetic push to get them to leave the metal. One such possible method for pushing electrons off metal is by using light, the photoelectric effect.

    Einstein looked into the photoelectric effect in detail and found some strange things. First, if he used light that was too red (low frequency) then it didn't matter how bright the light was, it wouldn't produce ANY photoelectric effect. Second, the higher frequency light used the faster the photoelectric electrons were (more energetic individual electrons) and for monochromatic light the electrons were all the same speed (uniform energy for uniform frequency). Third, increasing the brightness of the high frequency light did not change the energy of the electrons, just the number of ejected electrons.

    These strange observations indicated that the energy in light came in discrete packets (quantized) whose energy is proportional to the frequency of the light, and the ejection of an electron from the surface is due to the interaction of one packet with one electron. Increasing the brightness increases the number of the packets.
  6. Aug 27, 2013 #5
    If there was everyday 'intuition' behind physics, anybody could it! As Dalespam described, before Einstein everybody was 'stumped'; nobody even knew about 'discrete' 'quantized' science.

    It turns out that a fundamental aspect of quantum mechanics, things on a small scale, is that stuff happens in discrete amounts, not continuous ones, as in classical physics. It's often called a 'quantum of action'...now Planck's constant.

    A good way to get a feel for this, but not necessarily WHY it is this way [which nobody knows]
    is to check out the subject Planck's constant...Wikipedia describes Max Planck's discovery this way:


    If you would like some further insights, check the same article and read about Planck's black body radiation work which led to the above insight:

    Planck had a theory that didn't work so well, then

    So Planck didn't fully understand what he had done ...which was to revolutionize science!
  7. Aug 30, 2013 #6
    Here it's energy of EMR comes in packets called quantum (photon generalized for lught)

    each photon has and equivalent energy given by sir planck's equation


    where λ wavelength of photon
  8. Sep 25, 2013 #7


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    The word "quantized" is often used, unfortunately, to connote the term "discrete" even though "quantization" refers to something far more general than "discretization".
  9. Sep 25, 2013 #8
    No sound bite will quench your thirst for understanding this very crucial point. You really would have to learn the math from a good book about the introduction to quantum theory and still there is a pretty good chance you would be left unsatisfied.

    With that said, let me try to help even if just a little bit.

    First you must realize that the size of the packets depends on the specific kind of radiation. The shorter the wavelength of the radiation the larger the amount of energy in each packet. These packets are called photons. You may produce, absorb, transmit, etc... only integer number of those photons. There is no such a thing as half a photon just as there is no such a thing as half an electron or half a proton, etc...
  10. Sep 25, 2013 #9
    Have you a peer reviewed source for such statements? Those posted have nothing to do with quantized energy...like photons. A wave packet does not 'expand' and nor is it a 'sphere'.....You are probably thinking of a point like light source such as a light bulb from which light [energy] emanates in a spherical shape.


    In fact, individual photons [packets, quanta] CAN be emitted and detected....they ARE 'distinct entities'.....[just as are electrons, a different form of quantized energy].... for example a single electron typically absorbs a single photon..... All elementary particles have point-like interactions in the Standard Model …..When not interacting the size of the photon probability distribution depends on its environment....

    All this is rather subtle and whether 'particles' or 'waves are 'real' has been debated in these forums.
  11. Sep 25, 2013 #10


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    Hi, DGonzo2015!

    When I milked a dinosaur the milk came in packets. No, seriously, you've got good answers above - Planck's work on blackbody radiation and the photoelectric effect. Here are some additional pages which might be helpful:

    Problem 1: Blackbody Radiation (The problem - the "ultraviolet catastrophe")
    Solution 1: The Planck Hypothesis and Photons: The Quanta of Light

    Problem 2: The Photoelectric Effect (The problem)
    Solution 2: The Photoelectric Effect (The solution)

    The Photoelectric Effect (image):


    I hope it's helpful. If you got further questions, don't hesitate to ask!
  12. Sep 25, 2013 #11
    nobody knows...what we do know is that scheme works in this universe.
  13. Sep 26, 2013 #12


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    I'm somewhat uncomfortable using words "packet" and "quantum" interchangeably. "Packet" implies internal structure while a "quantum" is unbreakable.
  14. Sep 27, 2013 #13
    i didn't understood it well
    whatever i've said this above on my knowledge of chemistry atomic structure so may be - i be wrong
  15. Sep 27, 2013 #14


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    I've never seen it that way personally. Packet, to me, implies that it comes in discrete "chunks", like a package in the mail. You never receive half a package, only a whole one. (And if you do, the mailman owes you some money)
  16. Sep 27, 2013 #15


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    Usually it's one of "PF Patrons" I who reminds others that you cannot apply every day analogy to quantum mechanics :). Nothing is really wrong with "packet" (until you try to open it and you can't - it's a photon). I guess, it's commonly used in this context. WannabeNewton's also made a comment in this direction.

    But it's irrelevant when you explain photoelectric effect...
  17. Jan 13, 2016 #16
    it means to say that mass and matter have energy pushing called gravity and it makes package
  18. Jan 13, 2016 #17
    it is an extension of the 'atomic'...'particulate' aspect of nature. Electric current is a stream of particles but in normal use we are not aware of the 'particle' nature of electric current.
    Water flowing from a tap is a stream of water 'particles'..drops
    Light energy from a bulb is a stream of 'particles'....photons although we are not normally aware of the particle nature. Photons can be seen as individual entities in the granular images from night vision devices.
    Gamma radiation is a stream of gamma photons, these 'particles' have enough energy (size) to be detected as individual particles in a geiger counter
  19. Jan 13, 2016 #18


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    Energy is not equivalent to size. Gamma ray photons simply have enough energy to ionize the gas in the geiger counter's tube.
  20. Jan 13, 2016 #19


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    I'm sorry but I can't even begin to make sense of your post. Needless to say, this is not what quantized energy means.
  21. Jan 13, 2016 #20


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    @lucindawriter and @lychette, you are posting in a thread that's over 2 years old. That's called "necroposting" and is discouraged, especially when the person who started the thread hasn't even been to this forum in over a year. If you have questions about something in an old post, it's better to just start a new thread. We all do this from time to time, especially when we're new to the forum, because after all, who remembers to look at the date of the last post.

    EDIT: Drakkith, you are encouraging necroposting. Bad Drakkith !
  22. Jan 19, 2016 #21
    thank you for this....sorry ..was not really responding to the original post
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