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I have been thinking about different forms of energy and ways to define them, but I realized that most elementary forms of energy are waves, such as light (a wave in the electromagnetic field). Waves are a transfer of energy, so does that mean light is a transfer of energy? Or is light itself energy?


marked as duplicate by safesphere, stafusa, John Rennie energy Aug 7 '18 at 4:49

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Waves are a transfer of energy, so does that mean light is a transfer of energy? Or is light itself energy?

Light can be said to have a certain amount of energy. For example, when describing light as a collection of particles (photons) the individual photon's energy is equal to $hf$, where $f$ is the frequency of the light and $h$ is Planck's constant.

It is incorrect to say that light is energy. Rather, it is correct to say light "has" or "carries" energy.

Similarly, light can also be said to "have" a certain amount of momentum. It would be similarly incorrect to say that light is momemtum

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    $\begingroup$ I think the fact that the photon is its own antiparticle clouds the issue. No-one would say an $e^+e^-$ pair is energy, but like light they can just appear when there is sufficient energy available. $\endgroup$ – JEB Aug 5 '18 at 22:55
  • $\begingroup$ So when talking about "light energy", are we talking about the energy that light carries? $\endgroup$ – Cam White Aug 5 '18 at 22:56
  • $\begingroup$ @CamWhite, I would guess so. Depends on who's doing the talking... $\endgroup$ – hft Aug 5 '18 at 22:57
  • $\begingroup$ Is a flying ball energy or does it have energy? It depends on the type of energy in question. The ball has a kinetic energy and heat energy and many other types of energy. 99% of its total energy is the energy of gluons holding protons in the nucleus from flying apart. When we add all types of energy that the ball has, we can say that the ball is energy, the total energy it has, as in E=mc2. With light, the only energy it has is the electromagnetic energy with no other types. So light indeed is energy, a pure electromagnetic energy. $\endgroup$ – safesphere Aug 6 '18 at 4:04

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