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Some simple? questions on miscellaneous things?

  1. Jun 24, 2011 #1
    Some "simple?" questions on miscellaneous things?

    I don't know much about physics but I want to and I am starting to learn more about it, and quantum physics is already amazing me. I'm assuming these are "basic" questions...

    1. Why does light travel at c and not some other speed? Where does this energy (if any) come from that makes the photons travel?

    2. When you turn on a light, where are the photons coming from? and also why do the photons travel throughout the room instead of just staying stationary - (i mean why does light instantly travel instead of just staying still?)

    3. photons are emitted when a charged particle accelerates. so the light form a lightbulb when you turn it on is because the electrons are moving throughout the coils in the bulb, emitting photons?

    Last edited: Jun 24, 2011
  2. jcsd
  3. Jun 24, 2011 #2


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    Re: Some "simple?" questions on miscellaneous things?

    1A. Light travels at c because it is massless. By the equation F=MA (Which doesn't actually apply to photons, I'm just using it as an example), a photon's mass of 0 means that applying ANY force will have infinite acceleration. Moving the equation around yields A=F/M. Since M = 0, then dividing by 0 gives a result of infinity. (It's actually a null operation, as it cannot be done, hence why you can't use F=MA for photon) As for why the light moves instead of staying stationary, it has been observed and shown that light ALWAYS travels at c. It never accelerates as that would require it to have a speed of less than c at some point. In effect this means that upon creation they "instantly accelerate" to c, but in reality there isn't any acceleration, they simply always travel at c.

    1B. Photons are produced from various things. Chemical and nuclear reactions, heat, and other ways all produce photons. The energy of the photon is taken directly from whatever is producing it. For example, satellites and spaceships have to worry about overheating in space. This is because the only way to get rid of the heat is to let it radiate away as thermal radiation (Photons), as there is no air or any other material in space to carry the heat away like the air does for you and me here on Earth. The photons take the energy of the heat with them when they leave, as they are created from this energy.

    2. The photons are produced from the heating of the filament (the wire inside a lightbulb) by electricity. Look up Black Body Radiation on wikipedia for more info on that. In the case of florescent lights the photons are produced when the gas inside the lightbulb gets rid of the energy that is introduced when you flip the switch and electricity flows through it. The electricity causes the electrons in the gas to leave their orbitals around the nucleus. When these free electrons come across another nucleus that is missing electrons they can be captured again. When the electrons are captured they lose the energy they gained earlier, which is lost in the form of photons of visible light. This all happens VERY quickly in a light.
  4. Jun 24, 2011 #3
    Re: Some "simple?" questions on miscellaneous things?

    Here is a good explaination of light being made from all sorts of things


    the rest of the site is good as well
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