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Homework Help: Electric Field and Potential difference

  1. Jul 24, 2015 #1
    Hey guys, I have a problem that I really have no idea what to do.

    It was discussed in class that we do not need to know how to integrate or use the dot product-- any of the complex stuff.

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

    The electric field in a given region in space is given by (3 i - 1 j) x 10^5 N/C. Find the potential difference between points a (3, 1) and b (7, -1). The coordinates are in mm

    2. Relevant equations

    All I have is V =kq/r but I'm not sure what to do with this

    I also know that V=-E*r = kq/r2 - kq/r1 because the field is not uniform.

    3. The attempt at a solution
    I drew out a chart and plotted a and b and the marked out where the unit vectors ultimately lead to..
    I don't actually know what the question is asking and where to start.

    THanks in advance for your help.
    Last edited: Jul 24, 2015
  2. jcsd
  3. Jul 24, 2015 #2


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    This is not applicable to your problem. It is the potential from a point charge q and you are dealing with a homogeneous electric field.
    The field you have been given is uniform. Also, there are not charges involved in this problem.
  4. Jul 24, 2015 #3
    Ok so charges aren't involved.
    And if the field is uniform I would use: (Delta)V=-E*(delta)r
    But how do i get the field E with all these unit vectors?
    Would I just plug in the differences of x and y coordinates of point a and b into (3 i - 1 j) x 10^5 N/C to find the field?
  5. Jul 24, 2015 #4
    The true relation between ##V## and ##E## should be ##\Delta V=-\int E\cdot dl.## In this case, for ##E## is a constant vector, as you said, ##\Delta V = -E\cdot r.##
    So you have to find out the displacement between the two points, of course it should be the vector parallel to the electric field ##E.##
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