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Defining Light and Electromagnetism in simple layman's terms

  1. Apr 9, 2015 #1
    The way I have interpenetrated this phenomena without technical jargon is that:

    Light is basically waves or ripples of the + and - charges of the electromagnetic field which permeates the entire universe. This is very similar to sound rippling through a field of air molecules.

    These waves can be absorbed by matter via electrons in packets or chunks called photons, this absorption creates heat as it gives the atoms more energy than they had, this is responsible for how things heat up when left in the sun and also for how EM radiation waves are produced in the first place as the atoms release energy or mass when given too much of it. Photons can also be re-emitted in the case of mirrors etc. The absorption of a certain frequencies of light and not others is also what is responsible for color.

    The atoms release electromagnetic frequency vibrations because the electron and its nucleus oscillate there magnetic and electric fields in sync... one after the other, which creates the fluctuations of waves of the electromagnetic field.

    electromagneticjavafigure1.jpg

    These electromagnetic waves or "field distortions" can be channeled through spiritual mediums... just joking, they can be channeled through the pupil into the back of retina and the receptors transfer the ripples of the EM field charges into electro-chemical neural impulses which the brain somehow miraculously forms orders of neural connections which appropriately create a trustworthy conception of external reality.

    But what's the difference between electric, magnetic and electromagnetic fields? Both the electric & magnetic fields are perpendicular to each other & to the direction in which they are propagating in physical existence. EM waves basically replicates itself from each cycle of the electric field and then unto the magnetic field and then to the electric field and so on like in the picture above, and so this results in what we experience as light, the two fields fluctuating together one after the other.

    But what creates the fields? Electric fields result from the strength of the charge while magnetic fields result from the motion of the charge, or the current. So every atom has an electrically charged strength and an electrically charged motion.

    But why do EM fields exist through the universe though? Two electrically charged particles will experience a force due to their charges no matter what the distance is between them, So even if intergalactic space was completely empty (which it isn't) there would still be an EM field because matter exists somewhere in the universe.


    Is this all accurate? The question I have now are: What creates the positive and negative charges in the EM Field? In other words, Why do electric and magnetic fields vibrate on there own? I thought a field was something static and not moving like air and then sound is impressed into it.
     
    Last edited: Apr 9, 2015
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  3. Apr 9, 2015 #2

    Simon Bridge

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    Charges do not permeate the entire Universe - charge is quantized, so there are gaps between lumps of charge ... and light can cross regions of zero charge. The analogy with sound waves is just that, an analogy. It is not great since sound requires a medium for travel while light does not.

    Charge and Fields are different ways of describing the same thing - there is no simple layperson description of electromagnetism.

    It's misleading.

    I don't think anyone knows ... charge is a property of matter and EM fields are a way of describing electromagnetic interactions. In QFT the EM field is from photons (light) but that model has the photons as "excitations" of a quantum mechanics field and the whole thing vanishes in a mathematical chicken and egg game.

    This is a part of physics you can only understand through the mathematics.
     
  4. Apr 9, 2015 #3
    If it has no charge then what are the waves in the field? What are we referring to as charge then in that respect? Is it charge of the field or something else? If it is charges in the field then why are there gaps between the charges?

    From what I gather light needs an electric field and a magnetic field for it to be a wave in... so wouldn't that mean the fields themselves are the medium?


    How so?

    Yes, but there seems at least some ability for standard English to grasp these concepts even if they are vague in transferring an understanding of the truth at hand. So I am trying to gather what I can.
     
  5. Apr 9, 2015 #4

    Simon Bridge

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    Maths. The electromagnetic wave is not usually thought of as a wave of anything.
    The numbers illustrate the strength of the electromagnetic interaction at different places and times.

    Nothing - there is no charge so there is no need to refer to anything as charge.
    If you check the electromagnetic ave equation you will see that the quantity "charge" does not appear anywhere.

    .. not in the same sense as the air is the medium for sound waves or water is a medium for water waves.
    So no: that is not what "medium" means in this context.

    Light is not a wave in an electromagnetic field, it is electromagnetism.

    The analogy you are using has a number of misleading aspects - the need for a medium as part of the description is probably the most problematical of them.

    I agree that it seems that way, and I sympathize, but don't be fooled: that is a path ensnared with pitfall and djinn. You can get a hand-wavey pop-sci type of description that may be good enough for entertainment purposes but there are already lots of those so why not just use one of the others? You are better off looking for ways to take the interested layman from their current state of knowledge to a closer understanding rather than trying to produce as close a description as you can while sticking to their current understanding. Look at the common misunderstandings that lead to pseudoscience to see what sort of descriptions to avoid.

    For a quickie off-the-cuff about the wave model I usually start telling people to put luminescent ping-pong balls in a swimming pool and turn out the lights ... you see the balls bobbing about: electromagnetism is like that, the balls are kinda like charges, only there's no water.

    That said - Feynman does a decent job describing light, using lay language, for the particle model: you may want to add those to your collection. The quantum description of light is currently the most complete one and most amenable to a lay-language description.
     
  6. Apr 9, 2015 #5

    sophiecentaur

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    The concept of a Field is a very difficult one and people tend to assume they know what it involves. As Simon says, a Field is 'just Maths' because it just describes what will happen to a charge (or mass) at a certain point in space. Using the idea of Fields, means you can stop worrying what has caused the field and just deal with it in the region you are looking at. With an EM wave, there need be no actual charges, anywhere nearby (could be 100000 light years away); varying fields in one place will just cause varying fields in another. (That's very sophisticated and needs a lot of getting used to.)
     
  7. Apr 9, 2015 #6

    ZapperZ

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    Again, as I've posted elsewhere in response to others who put forward their own explanation, try and do this:

    "If this is true, then....."

    If you think that there are positive and negative charges oscillating in an EM wave (i.e., if your model is true....), then I should be able to separate them out! After all, they have opposite charges. So send this EM wave into a static electric field, and by all accounts, I should be able to separate them out from the EM field, no? Do you think this has been observed? Do you think your model is consistent and agrees with all our observations?

    EM wave consists of oscillating electric and magnetic fields, not oscillating charges. It requires an external source of field to cause charges to oscillate like that. Visit your neighborhood synchrotron light source if you don't believe me, and ask how the undulator and wiggler insertion devices work. The presence of oscillating electric and magnetic field is less mysterious and less problematic than the presence of oscillating charges in your model.

    Secondly, you also have ignored the fact that I can have varying geometry of electric field, depending on the boundary conditions. I can have an oscillating E-field in the z-direction and an oscillating magnetic field in the theta direction (as in a cylindrical coordinate system). This is a common geometry (a TM01 mode) in accelerating structures for particle accelerators. And there are LOTS more different geometries. The boundary conditions that allow for these types of EM wave to exist all obey the boundary conditions that E and B field must obey, but not necessarily what charges will obey.

    It might be useful if you look a bit more into EM wave in waveguides and see why your model fails.

    Zz.
     
  8. Apr 9, 2015 #7

    sophiecentaur

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    In a waveguide, there are, at least some charges moving about along the walls of the guide, which could support his misconception. But in a free wave, that was generated zillions of years ago, in a part of a star that has long since disintegrated, where are the charges?
     
  9. Apr 9, 2015 #8

    ZapperZ

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    But those are induced charges, not "source" charges, i.e. they are not part of the EM wave. Furthermore, when one solves for such boundary conditions in waveguides, one seldom (never?) considers these wall charges/current. Only those of us who work with such accelerating structures worry about wall currents and induced wakefields.

    Zz.
     
  10. Apr 9, 2015 #9

    sophiecentaur

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    Chicken and egg, here, I think (in the context of the OP, at least). But isn't that the same for any wave, radiated from an antenna, atom or reflecting surface? Fact is that, outside the conducting structure, and in a vacuum, there are no charges actually 'in' the wave.
     
  11. Apr 9, 2015 #10

    ZapperZ

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    Not sure why we are having this discussion especially when the OP is not here.

    First of all, it is not a chicken and egg issue. There is a cause-and-effect! You solve the poisson equation inside the waveguide with no charge, and match the boundary condition. Is this not explicit enough that there are no charges in the WAVE itself, which is ".... in the context of the OP, at least...."? Last time I checked, the OP isn't concerned with induced charges, just the actual EM wave itself having the oscillatory behavior.

    Zz.
     
  12. Apr 9, 2015 #11

    sophiecentaur

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    Surely charges are displaced in the metal surface due to the incident wave and they cause a reflected wave?? Which is the chicken and which is the egg? That's all I meant. But, of course, no atoms means no charges moving.
     
  13. Apr 9, 2015 #12

    ZapperZ

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    Yeah, ok? So the wall currents can generate its own field. Didn't I mentioned the structure's "wakefield" just now? There are still no charges in the cavity volume, which is where the EM wave reside! That's my entire point!

    I can even do one better. Turn off the EM field, and the cavity will still "ring" for a short time, depending on the Q of the cavity! Have we made this sufficiently complicated enough that it is irrelevant to the original question, or would you like to continue?

    Zz.
     
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