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Is light a particle or a wave?

How does classical physics account for light (particle or wave) and how does quantum theory account for light?


  1. It is both a particle and a wave and quantum theory accounts for light by electrons jumping from orbitals releasing photons (Particles of light)

  2. Classical Physics describes light as a self propagating electromagnetic wave. And experiments do demonstrate that light acts like a wave, it interferes with itself like a wave. Because light interferes with itself, it must be a wave.
    Quantum Physics describes light as quantized packets like particles. The photoelectric effect is the quintessential experiment that demonstrates that light acts like it is made up of particles and not waves. In the photoelectric effect, high energy light knocks electrons off of metal. As the frequency of the light is decreased, at some critical frequency, the light will stop knocking electrons off the metal. If the light was a wave, the energy incident upon the metal should be able to be increase by increasing the amplitude of the wave (or the intensity of the light). BUT when the intensity is cranked up, no electrons get knocked off. This can only be true if light is not a wave.


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