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Electrostatic forces

  1. Jan 18, 2016 #1
    Hi, two questions:

    Does the same energy put into an attraction force give the same force as a repulsion force? Im wondering if one is measuring slightly weaker than the other.
    ie. If I measure the positive/negative attraction force, is the positive/positive repulsion force as strong when given the same energy input?

    Also, has anyone tested these forces within a positive or negative environment? as I wonder if a repulsion force actually exists, that maybe its actually an attraction force to the outer more naturally charged environment.

    thanks, Seb
     
  2. jcsd
  3. Jan 18, 2016 #2

    ZapperZ

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    Why don't you try and calculate it, because it isn't that difficult. Put a positive charge, say at the origin, and then bring (i) another positive charge from infinity to a location r away from the first charge and (ii) bring a negative charge (same magnitude as in (i)) to the same location r away from the first charge. What is the work done in each case? Other than the difference in "sign" (i.e. work done by the field versus work done onto the field), do you expect there to be a difference in magnitude of the work done?

    Zz.
     
  4. Jan 18, 2016 #3
    obviously the simple formula says its the same, but does experiments agree?
     
  5. Jan 18, 2016 #4

    ZapperZ

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    It isn't just the "math". The math is based on a physical foundation, which is the classical Maxwell equation. This means that this is physics, and it has been tested and verified, at least within the limits of its validity.

    As far as we know, there is no asymmetry between the two situations that you described. But there is another aspect here that you seem to not have noticed. The presence of an "attractive" or "repulsive" force is really irrelevant. The "test charge" that I used in my example really isn't aware of that charge that is at the origin. All that matters here, if you did what I asked you to calculate, is that there is an electrostatic potential field V(r). This is the field that the test charge sees, regardless on how that field was created.

    So what you are really asking, without you realizing it, is if a positive and negative charge behave differently in the same potential field. Let's just say that if it does, there's a whole new physics here that we don't know of from classical E&M.

    For your information, the Advanced Photon Source (APS) at Argonne started life using positrons as the charge that goes around inside the synchrotron. A few years after that, they switched to electrons. Do you think they saw any difference in the physics, other than a change in sign of the charge?

    Zz.
     
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