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!

I What causes oscillations in EM wave fields?

  1. Sep 1, 2016 #1
    I've been trying to understand what an electromagnetic wave is, and have spent quite a while now reading around and piecing different bits of information together to try and get an answer. I haven't yet found an answer to my title question. It might just be because I have a lack of understanding.

    I have learnt that the sinusoisal pattern of waves is due to the oscillation of electric/magnetic fields. What causes this oscillation? What is actually happening?
  2. jcsd
  3. Sep 1, 2016 #2


    User Avatar

    Staff: Mentor

    Oscillating electric and magnetic fields are ultimately produced by oscillating charges or currents. For example, a radio transmitter is basically just a wire or collection of wires that carry oscillating electric currents.
  4. Sep 1, 2016 #3
    Isn't that because a wire is a ready made medium, full of electrons which are passing energy along the wire without moving forwards themselves? Hopefully I've remembered this correctly. If so, how does this relate to photons and empty space? Thanks.
  5. Sep 1, 2016 #4


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

  6. Sep 1, 2016 #5
    Lets properly define what we need because I think we have a word salad here. We have electric fields and magnetic fields, both are created and changed by charges. For magnetic fields it would be moving charges, so you can be neutral and still feel its effects, and the electric field is for all charges, stationary or moving.

    Electrons create an electric field, on their own, this field is unchanging. When they move around however, the field has to change as well, and in the process also create a magnetic field (only a little fib, again we don't need QM to explain EM waves), so now even neutral bodies carrying currents can be affected by it. If you moved the electron back and forth and measured the field, you'd see the field oscillates with a lag.
    If you put a series of sensors in a line you'd see a wave because the lag increases with distance.
    You see the field is what oscillates, if the electric field oscillates, so does the magnetic field which is dependent on changing fields and moving charges.
    Using maxwell equations you'd see that in free space, the wave propagates itself at the speed of light, so it will never stop until it loses energy, how? when it causes charges to move.

    The oscillation IS the EM wave itself. What starts the wave is moving charges and changing fields.

    Photons are the product of finding out that the wave has its energy quantized. Which means it is some amount multiplied by an integer greater than zero if a wave is present. Photons are there to be the quanta of EM waves, and charged particles will emit photons to interact with one another.
  7. Sep 1, 2016 #6
    I had no choice but to arbitrarily select a prefix option, and it's not something that is taught in high school.

    I hoped that if I asked a specific question, someone would be able to give an answer in words I will understand.
  8. Sep 1, 2016 #7
    Sorry posted before I saw the previous answer.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted