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Plot help, Culobs Law

  1. May 9, 2007 #1
    1. The problem statement, all variables and given/known data
    Okay here is the deal, I have made a experiment, and now I have some probs, getting the right stuff from gnuplot.

    If I isolate qQ in Culombs Law I get:qQ = F*4*Pi*e0*r^2:
    Here e0 is the permittivity of free space
    r is a constent, the distence between the charges.
    If I plot F*4*Pi*e0*r^2 as a function of qQ, the slope of the linear function schuld be one, right?.
    I have the folowing data:

    qQ F*4*Pi*e0*r^2 delta g(x)

    3.94e-15 2.129e-15 2.2e-16
    2.28e-15 7.413e-16 8.1e-17
    1.17e-15 3.177e-17 3.2e-17
    7.38e-16 -3.601e-16 4.8e-17
    4.31e-16 -6.248e-16 7.1e-17
    3.08e-16 -7.307e-16 8.0e-17
    2.46e-16 -8.261e-16 8.9e-17
    1.85e-16 -9.002e-16 9.6e-17
    1.23e-16 -9.320e-16 9.9e-17

    So I want to fit them to a linear function. I load this plot command:
    #Nu definere vi funktionen f(x) som er den vi vil fitte efter:

    fit g(x) "data.txt" via h,b

    set xlabel "qQ [C^2]"

    set ylabel "(F*4*Pi*e0*r^2) [C^2]"

    set title "Kraftens afhængihed af afstanden mellem 'punkt ladningerne.'"

    plot g(x), "data.txt" w e

    And then i get a fine plot, but also this in my fit log:
    Wed May 09 16:19:02 2007

    FIT: data read from "data.txt"
    #datapoints = 9
    residuals are weighted equally (unit weight)

    function used for fitting: g(x)
    fitted parameters initialized with current variable values

    Iteration 0
    WSSR : 9 delta(WSSR)/WSSR : 0
    delta(WSSR) : 0 limit for stopping : 1e-005
    lambda : 0.707107

    initial set of free parameter values

    h = 1
    b = 1

    After 4 iterations the fit converged.
    final sum of squares of residuals : 5.99386e-031
    abs. change during last iteration : -2.37224e-019

    Hmmmm.... Sum of squared residuals is zero. Can't compute errors.

    Final set of parameters

    h = 1
    b = -1.20129e-015

    I bellive the problem is here:
    Hmmmm.... Sum of squared residuals is zero. Can't compute errors.

    I want gnuplot to give me uncertenties on the free values h and b, but it docent.
    And got no clue on how to fix it.
    So what is the problem, anyone?
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. May 9, 2007 #2
    And now I got the titek wrong :SS:
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