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Homework Help: Electric Fields

  1. Nov 8, 2006 #1


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    Gold Member

    Hey. Was just reading through some notes, and found the equation for the strength of an electric field:

    E = \frac{F}{q}

    Im a little confused. How can an electric field have a single value that can define its strength, if the force, F, on the test charge, q, is dependant upon the distance of the test charge from the source charge?

    Thanks in advance,

    PS. This isnt a homework question, just something that i came across that had me confused.
  2. jcsd
  3. Nov 8, 2006 #2
    E = F/q is specific to a point in space with a given force. Electric field, relative to a point charge does depend on distance in the same way you would expect, E = q/r^2 . The only time you would get a constant E that applied to every point in a space would be in a situation like that which occurs between the plates of a parallel plate capacitor
    Last edited: Nov 8, 2006
  4. Nov 8, 2006 #3


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    ok. So really, at a basic level, there is no way to state the strength of an electric field, without it being relative to a specific point?
  5. Nov 9, 2006 #4


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    Staff: Mentor

    The electric field is just that -- a field. You represent it with E field lines. The E field is a vector field. At any point in space, E has a vector value that points in the direction of the E field lines in that area.
  6. Nov 9, 2006 #5


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    Ok makes sense. Thanks for the help.
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