1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Question about light as an EM wave

  1. Aug 17, 2015 #1
    I'm so puzzled right now (sorry if I'm being stupid or something) , we can clearly see that EM waves oscilate the electrons in a conductor,they start vibrating and create EM waves again and these EM waves oscilate some other electrons and again they create another EM wave.

    All EM waves are supposed to work like that and we use this interesting phenomenon in radio,TV,microwaves,etc.
    And of course all EM a waves have different "abilities" such as reflection,refraction,absorption,diffraction,interference.

    Recently I've read that light itself,because of being an EM wave,oscillates electrons and it states that because of this oscillation of electrons light can reflect and be absorbed by other bodies (not sure about refraction).
    Like when light reflects,these oscilating electrons create EM waves thus we see reflection.

    And there is this difficult photon theory that i don't even really understand,some people state that this oscillating theory is incorrect but I don't understand how if light IS considered as an EM wave,so it IS supposed to oscilate electrons and create EM waves.

    I'm really puzzled.
  2. jcsd
  3. Aug 17, 2015 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    The em waves are an "emergent phenomenon" due to photon interactions.
    The understanding you have of the interaction of em waves with electrons is very simplistic and does not give you the whole picture.
  4. Aug 17, 2015 #3
    This the easiest way to look at it, just as a starting idea.
    Electrons are fundamental particles, mostly they exist in layers or shells around an atom's nucleus.
    Photons also are fundamental particles, but they are not part of atoms, they are carriers of energy, 'EM radiation'.
    When a photon encounters an atom, it may be energetic enough to kick an electron into a higher energy state, the photon then no longer exists.
    Electrons can also drop to lower energy states, and in doing so they emit a photon.
  5. Aug 17, 2015 #4


    Staff: Mentor

    You don't really need to know anything about electrons or photons to understand the vast majority of "everyday" EM. If you have ever rubbed a balloon on your hair and stuck it to a wall then you are familiar with charge and the electric field. If you ever got shocked then you are familiar with electric current. If you ever used a compass then you are familiar with magnetism. All that remains is to learn the math that ties them all together.
  6. Aug 18, 2015 #5
    It's just all EM waves pretty much act the same way - they cause oscillations of electrons,right?That's why we get more EM waves and heat,all due to oscillations.

    But there is this photon theory of light that messes me up that states something like photon gets absorbed by the electron then it gets excited and goes to a higher energy state and then it emits the photon and goes back to it's first lower energy state.Does this even have to do with refraction and absorbtion of bodies?Like I know that it explains why reflection occurs but refraction and absorbtion?

    All I'm trying to understand is why EM waves refract,reflect and get absorbed by other bodies,I thought that the oscillation of electrons due to EM waves pretty much explains all this stuff,but there is also this photon theory that looks at this in a brand new way.

    I've seen a lot of forum pros here stating that oscillation theory is BS and it's all about photons but I can't understand why...
  7. Aug 18, 2015 #6


    Staff: Mentor

    Well, it isn't just electrons. It is any charged particle, an electron, a proton, an ion, a macroscopically charged object, etc. Also, it is not just oscillations, you can also exert steady forces and torques.

    Oscillations of electrons is one small part of EM phenomena.

    It can be used to explain absorption and emission spectral lines, but it is not useful for explaining reflection, diffraction, or any of the other macroscopic wave phenomena.

    Again, I think that the classical model is sufficient for the vast majority of EM phenomena that you are familiar with. I would recommend ignoring all of the quantum stuff for now until you have mastered the classical treatment of EM.
    Last edited: Aug 18, 2015
  8. Aug 18, 2015 #7
    So is it safe to assume that reflection,refraction and absorbtion happen due to the EM nature of light,because EM wave of the light makes contact with charged particles inside of a conductor?Like absorbtion can be imagined once again as acceleration of charged particles because of light's EM wave inside of the conductor,due to this they start hitting each other and gaining thermal energy,like microwave explanation,right?

    Or am I totally wrong about this?It's just i see that some people explain such wave phenomenas in this way and other people are trying to explain it with the photon theory.
    I believe that on some old thread you have said that it has to do with photon interaction,that's why I'm so puzzled right now...
  9. Aug 18, 2015 #8


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    This only describes what happens when a photon interacts with an isolated atom (in a gas). When an em wave interacts with a lump of solid or liquid, there is not a simple one-to-one electron - photon relationship. That's because the atoms in a solid are so near each other that all the outer electrons over a large region of the solid are involved. The schoolboy Hydrogen Atom model cannot be used to explain more complicated systems.
  10. Aug 21, 2015 #9

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    The photon description of light... interactions with charged particles, reflection, refraction, etc. is well handled in a non-mathy way by Richard Feynman... one of the guys who got a Nobel prize for figuring it out.
    Please see:
  11. Aug 21, 2015 #10


    Staff: Mentor

    There is nothing wrong with using photons to explain light. It is just usually more complicated that necessary.

    It is like using a rotating reference frame to solve an inclined plane problem. Sure, you can do it, but it doesn't help and it does make things much more complicated.

    I prefer to use the simplest valid explanation, don't you?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook