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Question regarding electromagnetic interaction

  1. Mar 29, 2008 #1
    I attach a question (PDF-file) which I found in an old physics book, I printed the question and re-generated the drawing which were a bit hard to scan.

    Can anyone answer the attached question, I think I know the answer but I want to be sure.



    Attached Files:

  2. jcsd
  3. Mar 29, 2008 #2


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    Staff: Mentor

    Tell us what you think the answer is, and your reasoning, and then we can either confirm it or rip it to shreds. :biggrin:
  4. Mar 29, 2008 #3
    Well, the obvious answer is that the plate experience a force downward.
    The thing that puzzles me is whether the accelerated electrons are suppose to generate an ossilating electric field to both diretions (up and down) or a unidirectional electric field due to the fact that they are only accelerated in one direction.

    Now, am I right ?
  5. Mar 29, 2008 #4


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    There will be a non-oscillating electric field E_a in the direction of the acceleration, exerting a downward force on the positively charged plate, as you say.
    There will also be an electric field E_b pointing toward the electron, which would exert a leftward force on the plate. E_a falls off as 1/r, while E_b falls off as 1/r^2, so each will dominate at different distances.
    An oscillating charge radiates an oscillating field, but this charge is not oscillating.
  6. Mar 30, 2008 #5
    Thanks Pam
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