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Electric field strength on particles of various distances

  1. Jul 5, 2017 #1
    There is no math in this one! I just wanted to know if I had the idea correct.

    1. The problem statement, all variables and given/known data

    If I have two positively charged particles at a distance between them that a field is produced between and around them, will test particles that repel away be solely a function of their distance from the charged particles? In other words, is the field strength only dependent on distance from particle?

    Where the two fields meet and field lines become uniform, the flux is greatest there. Will the intensity of the field here still be dependent on distance from the charged particles?

    2. Relevant equations

    I see a relation between E = kQ/r2 and Φ=EA .

    3. The attempt at a solution

    Since Φ is dependent on E, which in turn is dependent on size of charge divided by distance squared, I believe that field strength is dependent on distance. Have I got this correct?
  2. jcsd
  3. Jul 5, 2017 #2


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    Dear chop&,

    It is a bit hard to extract your perception from this essay !
    A few notes:
    A charged particle generates a field all over the place.
    Another charged particle does so too. The fields 'meet' everywhere ! And they simply add up, but:
    Electrostatic fields are vector fields. So the field vectors must be added up (as vectors, of course).

    For your two identical charges casus the electric field looks like (picture from here)


    and what is shown are the field lines of the total field. Close to a charge the influence of the other charge is relatively small and the field looks like the field from a single charge. In the symmetry plane the horizontal components cancel and in the very center the total field is even zero (not the potential !).

    You don't say what these are. But they indeed have an E in common.
    Yes, you even wrote it out: E = kQ/r2. But you mean something else, perhaps ?
  4. Jul 5, 2017 #3
    I should have included a photo! Thank you BvU, that is exactly what I was looking at ;-)
    I guess I just wanted to be sure - when I first looked at this situation, I was sure of the field strength being dependent on distance from the charged particle, but then I started reading about flux and how flux was maximum at 90 degrees and I saw how there were two lines of force passing through the particle at the bottom and though, hmmm... maybe I don't understand the concept as well as I thought I did. So despite the two lines of flux - it is still dependent on distance from particle.

    Yes, the center is null because the two charges oppose each other. Interesting to note that the center is not at zero potential - I was curious about that when I was reading!! But I guess that makes sense, if you were to introduce a charged particle between the two, a new set of lines of force would rearrange the structure and charged particles would move - isn't that emf?

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