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Electric Field of an Electromagnetic Wave

  1. Apr 23, 2009 #1
    Hello !
    I have a very old doubt about Electromagnetic Waves, I hope somebody can help me.
    Is the electric field of an EM wave really an Electric Field?
    I mean, what is the difference between that E field and an Electric field produced by, for example, an electron?
    If we have an EM wave, polarized, with a ver very low frequency, then in some point of the space we will see a constant Electric field? like if it was generated by a charged particle or body?

    Thanks !!!
  2. jcsd
  3. Apr 23, 2009 #2
    There are two sources of an electric field E; a) the gradient of a potential (times -1) from electric charges, like electrons or protons, and b) the Faraday's law of induction (also times -1) as a result of the time derivative of a magnetic field in an encircling loop. Aside from the fact that only one of these can be a DC field, the two electric fields are identical, unless you look in a mirror. In a mirror, the sign of electric charges are unchanged, so the electric field is the same. On the other hand, the right hand rule in Faraday induction, if applied to the mirror reflection, will change the sign of the electric field in the loop. So unless you look very carefully, there is no difference between the electric field from real charges or from the curl E equation (in Maxwell's equations).

    To show that the Faraday induction field has the same effect on an electron as the electric field of static charges, study the physics of the betatron, invented by Professor Kerst at the University of Illinois in 1940 to accelerate electrons.
  4. Apr 23, 2009 #3


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    I think you mean the "Ausserordentlichhochgeschwindigkeitelektronenentwickelndenschwerarbeitsbeigollitron" thank you very much.
  5. Apr 24, 2009 #4
    Yes. The name "betatron" (a reference to the beta particle, a fast electron) was chosen during a departmental contest. Other proposals were rheotron, inductron, and even Ausserordentlichhochgeschwindigkeitelektronenentwickelndenschwerarbeitsbeigollitron, supposedly German for "extraordinarily high-speed electron producing hard work by golly-tron.". Maybe there should be an acronym, similar to FLAK.

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