Energy of photon [closed]








**Closed.** This question is [off-topic](/help/closed-questions). It is not currently accepting answers.
 
 






---








 This question does not appear to be about chemistry within the scope defined in the [help center](https://chemistry.stackexchange.com/help/on-topic).




Closed 8 years ago.








[Improve this question](/posts/32344/edit) 



What is a photon and how is its energy directly proportional to frequency of light (please don't tell that it is because $E=h\nu$ relation)?




A photon is a quantum of light. 


To explain more thoroughly, everything in the universe has elements of both particles and waves. So while light is usually thought of as a wave in classical mechanics, it also consists of particles. One photon is the smallest amount of light you can have while still having light at all.


The relation between the energy of a photon and its frequency (as well as how its particle nature was realized) was determined by Albert Einstein in a treatise on something called the photoelectric effect. The basic experimental set up was fairly simple. People had observed that, when shining light on a metal's surface, sometimes electrons would start popping out. The hypothesis proposed by classical mechanics was that this was proportional to the intensity of the light shining on the metal.


However, when the experiments were carried out, the results were a bit more surprising. The light had to be a minimum *frequency* before electrons were ejected at all. If the intensity of the light were increased at that frequency, more electrons would come flying out, but each electron would still individually have the same kinetic energy. If the frequency of the light was below the threshold, then no electrons would come out regardless of how intense the light was. And the higher the frequency of the light (once you got above the threshold frequency), the faster the electrons flew out.


So, Einstein realized what this meant: light had to exist as a particle as well as a wave. Each light particle (which he called a "photon") could interact with one electron at a time. Higher intensity light just meant more emitted photons, so the individual photon had to have enough energy to dislodge the electron from the metal surface. According to the experiments on the photoelectric effect, this energy was proportional to the frequency of the light, as noted before. When Einstein did the calculations, the constant of proportionality was $6.626\times10^{-34}~\mathrm{J~s}$, better known as Planck's constant and represented by the symbol "h."


The fact that this exact constant appeared in something seemingly completely different (the law for how blackbodies emit light) was a major basis for more investigation and eventually yielded quantum mechanics as we know it today.


 1