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Homework Help: Determining Coulomb's constant

  1. Jul 18, 2011 #1
    1. The problem statement, all variables and given/known data

    Determining Coulomb's constant through a force vs. separation distance graph.

    2. Relevant equations

    F = kqQ/r^2

    3. The attempt at a solution

    So, I'm a little confused about what I should do! We were shown a video of two charges moving towards each other. We were given force/distance data, and I used this to plot a graph. However, I need to make a straight line in the graph...which can be done by working with the equation u = 1/r^2. I've tried using the force values and the distance values but to no avail. I used the distance values as r and then sub those into the x-axis, which is what I did ... so should I simply try to change the scale of the graph ... or something else
  2. jcsd
  3. Jul 18, 2011 #2


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    Homework Helper

    Welcome to PF, uflash.
    So, you are trying to find the k, right?
    The usual approach is to make a graph whose slope is the thing you want to find. You must make F = kqQ/r² look like y = mx so you would choose x to be qQ/r² and y to be F. Then the slope will be k. That is, graph F vs qQ/r² and find the slope.
  4. Jul 19, 2011 #3
    if u =1/r2

    then F = ( KqQ ) u , which closely resembles the straight line equation y = mx +b.

    where F represents the "y" values, kqQ is the slope, and u represents the "x" values. In this case, the "b" value (y-intercept) equals zero.

    so , try substituting u= 1/r2 values into the x-axis to get the solpe .
  5. Jul 19, 2011 #4
    Thank you so much! That really cleared it up for me.
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