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What is light?

  1. Apr 23, 2010 #1
    Hello guys,

    Ok I read that light is an electro magnetic wave, but I don't understand what an electro magnetic wave is? I read wiki and seen diagrams but I don't get it. What do they mean light has an electric component, do they mean light is charged particles travelling, why does electric field create magnetic field? What is a magnetic field? Thanks :smile:
     
  2. jcsd
  3. Apr 23, 2010 #2
    light is an excitation of the EM field . Light is neutral it has no charge and a zero dipole moment. If i have a proton which has a dipole moment and charge if I accelerate it , it will radiate photons , I dont know if this is what your looking for.
     
    Last edited: Apr 23, 2010
  4. Apr 23, 2010 #3
    Thanks for the response :smile: I know how a photon is released from an atom. Why did you say it is accelerating? How is it constantly acted upon by a force?
     
  5. Apr 23, 2010 #4
    if we move a proton it will emit light , i am not sure if we have to accelerate the proton
    of that it just has to be moving. we could accelerate a proton with an electric field .
     
  6. Apr 23, 2010 #5
    Thanks again. Ok so if light is a bunch of neutral charged photons moving, then why is it called electro magnetic wave? Where is the electric component?
     
  7. Apr 23, 2010 #6
    I don’t really know the answer to your question , But an EM wave is a self sustaining electromagnetic field , I think Maxwell wondered if a an electric field can create a magnetic field then could that create another E field an so on ,
    And one of the solutions to Maxwell’s equations is
    c=1/sqrt(eb)
    where e= electrical constant and b is the magnetic constant
    he found that these EM waves traveled at the speed of light and he knew this was no coincidence and then he realized the must be related.
    Hope fully some one with more expertise will jump in an answer your question.
     
  8. Apr 23, 2010 #7

    jtbell

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    Staff: Mentor

    Electromagnetic radiation is produced by accelerating / oscillating electric charges, but it does not itself carry electric charge. After all, you don't become electically charged simply by standing in the sunlight, do you?

    Similarly, you produce sound waves by vibrating your vocal cords, but you don't have little bits of flesh from your throat flying through the air.
     
  9. Apr 23, 2010 #8

    Dale

    Staff: Mentor

    :surprised yuck!

    To the OP, it seems like you need to learn the very basics about Maxwell's equations. I would recommend starting with the Hyperphysics page:
    http://hyperphysics.phy-astr.gsu.edu/hbase/electric/maxeq.html

    Be sure to follow the links to each of the different laws.
     
  10. Apr 23, 2010 #9
    Thanks for the response :smile: So what I'm thinking is light is like an electric field between oscillating positive and negative charges. if electrons in the sun oscillate and send a light wave, what is the positive charge that the electric field runs up to?

    @Dalespam: Thanks for the link :smile: I'm not studying this area, this is just for interest.
     
  11. Apr 23, 2010 #10

    HallsofIvy

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    Science Advisor

    No! A magnetic-electric field itself does not have "charge", it is the field around a charged object.

    Also, in earlier post you seemed to be confusing "proton" and "photon". A proton has charge and accelerates. A photon does not have charge and never accelerates or decelerates- it is always moving at speed c.
     
  12. Apr 23, 2010 #11
    Thank you for your reply :smile: Ok now I understand that light is an electric field between charged particles that oscillate. So if a light ray from sun travels to earth. What are the charged particles involved to create the field? Charged particles on the sun and earth. Thanks!!

    Edit: I also don't understand why light doesn't need a medium to travel. In a vaccum there are no charged particles so how can light travel?
     
  13. Apr 23, 2010 #12
    If light is emitted by fields of charged particles , then from what field does a photon come from in an anti-neutrino neutrino collision.
     
  14. Apr 24, 2010 #13

    Dale

    Staff: Mentor

    If you are interested enough to ask the question on Physics Forums then you are interested enough to read the answer on Hyper Physics.
     
  15. Apr 25, 2010 #14
    I am curious then what causes the photon emission in a neutron anti-neutron
    collisions , from what EM field are they created .
     
  16. Apr 25, 2010 #15
    An electromagnetic wave has an E field and a B which are perpendicular to each other. But other descriptions explain light as a stream of photons.

    How do you marry a particle description with a wave description? Thats a question I would certainly like answered.
     
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