Where Do Photons Come From?

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Photons come from electrons that fall from one energy level to another, creating small packets of energy of distinct energy types. Discover the origin of photons with interesting information from a math and science teacher in this free video on science.

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Hi, I'm Steve Jones and I'm going to tell you where photons come from. Well photons, it sounds like a particle, but it isn't. But it isn't a wave either, it's a particle of waves or a wave of particles, I'm not sure which, but it originates and photons originate from energy changes within an atom. So you can imagine you got an atom with a nucleus, but it's not the nucleus we're interested in, it's the electrons which are flying around it. And these electrons are allowed to have certain energy levels. This is in the what's called the ball model after Niels Ball. So this ball model, which was postulated around the 1930's, suggested that electrons when they fall from one energy to another, cannot only do so in certain ways. They can only have certain energies. They can't have any old energy and they are said to be quantized. So if they are quantized, they fall from one energy level to another and they emit H new 01 we'll call it, that is H is Planck's constant and new is the frequency. This is a certain amount of energy where the difference in energy is equal to Planck's constant times the frequency. Now it doesn't matter if you don't understand that too much, but just remember that it depends strictly on that energy difference so it's only certain energies you can get. And this H2 is a photon, a little packet of energy. Well we can try to bundle the energy, you can call it a particle if you like because it sometimes behaves a bit like a particle and sometimes behaves a bit like a wave. Now obviously in this model, there can be various different falls, changed of energy like this, you can see I've got several here there can be many others too. I mean I could fall, it could fall from there to there. That is also producing a different photon of energy. And all of these different energy levels give us lots of different energies. And when you see a light burning, like a streetlight, it looks yellow, that's probably because it's sodium because sodium actually produces two very specific colors of yellow light which are very, very precise. It is not a general yellow color, it is two absolute distinct wavelengths of light. It is monochromatic, absolutely monochromatic and therefore this produces monochromatic bundles of energy. So sodium is typical of that but all materials when they produce light produce different bundles of photons and these photons have different energies which gives them different colors whether you can see them or whether you can't.

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