A photon means a packet of light energy (electromagnetic radiation in general). Light had been known as a wave but there are some situations where the wave picture of light is not able to explain some effects or occurances. Light then behaves as a stream of particles travelling at the speed of light. Each photon has energy E = h x f, where h is the plank's constant and f is the frequency of the corresponding wave. (Even when we consider light as stream of photons, we still talk about frequency of the wave. This is called dual nature of radiation). Total energy of the radiation will be the sum of energies of all the photons. As colours change, frequency changes. Violet has a higher frequency than red and hence the photon of violet light will be more energetic than that of red light.
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