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Why does a white photon create different energy photons in the prism. I have learnt that energy of the light is same after entering the prism. Then why does it break into seven colours photons who's energies are different. And how does it maintain the energy conservation. Does the energies of seven photons sum equalize the total energy of white photon?

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  • $\begingroup$ Are you sure there is a white photon? $\endgroup$
    – M. Enns
    Commented Mar 29, 2018 at 0:12
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    $\begingroup$ White light is a mix of different colors. The prism refracts different colors different amounts and separates them. $\endgroup$
    – M. Enns
    Commented Mar 29, 2018 at 0:17
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    $\begingroup$ There is no white photon. Nor a black one in case you wonder. A photon has a single frequency, that defined it's color. For white it is a mix of photons which if roughly equally distributed between the different colors gives you white. If you take Zed's prism below and use the outgoing light, and with mirrors bend each color so they come together again it will look white. Many photons $\endgroup$
    – Bob Bee
    Commented Mar 29, 2018 at 1:04
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    $\begingroup$ "A photon has a single frequency" - is this true? From what I've read here, a photon is an eigenstate of the photon number operator with eigenvalue 1. Taking a look at the linked FAQ, find: 'Thus a general photon is a superposition of monochromatic waves with arbitrary polarizations, frequencies and directions." $\endgroup$ Commented Mar 29, 2018 at 1:55
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    $\begingroup$ I took a quick look at that FAQ, and I don't understand it. What I can tell you is that in every presentation of QED that I have seen, photon states are by definition single frequency. There may be another way to look at things that I've not seen, but it seems the single frequency picture is certainly the most common. $\endgroup$
    – garyp
    Commented Mar 29, 2018 at 2:41

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Each photon is identifyed by its frequency, and there is no frequency perceived as white. A group of photons can be white, not one. Each photon (of different frequency) goes through the prism with a different trajectory but (assuming the prism does not absorb light) the same number of photons that come in, come out.

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  • $\begingroup$ "Each photon is identifyed by its frequency" - "According to quantum physics, monochromatic light of frequency 𝜈, such as the light emitted by a laser, is composed of photons of energy E=h𝜈, where h is the Planck constant. Polychromatic light, such as the light emitted by the Sun, contains photons of many different frequencies. However, each individual photon usually has a well-defined frequency and energy. Interestingly, the superposition principle of quantum physics allows for yet another version of polychromatic light: ..." $\endgroup$ Commented Mar 30, 2018 at 12:20
  • $\begingroup$ "... a single photon in a superposition of two discrete frequencies $𝜈_A$ and $𝜈_B$. In this case, neither the frequency nor the energy of the photon is well defined. In some sense, such a “bichromatic” photon can be thought of as having two different colors at the same time, only one of which would be revealed if the photon were measured by a spectrometer or detected by eye." - Viewpoint: Photon Qubit is Made of Two Colors $\endgroup$ Commented Mar 30, 2018 at 12:20

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