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Capacitance vs. Distance of separation

  1. Feb 4, 2008 #1
    [SOLVED] Capacitance vs. Distance of separation

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

    Hi, I am suppose to make a capacitance vs (1/d) graph. I understand that the relationship between the capacitance and distance between the plates is inversely proportional and that it does not produce a straight line.
    My instructor mentioned that when graphing the C vs 1/d graph it would have a negative slope, but when plotting the point in excel I get a graph with positive slope.

    3. The attempt at a solution

    [​IMG]
    1/d is on the x axis and C is on the y axis. Does this graph seem correct, or should I go with the graph that has the negative slope which I can only get by using a C vs d relationship.
     
  2. jcsd
  3. Feb 4, 2008 #2

    Hootenanny

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    In general the independent variable (the variable which you are controlling) is plotted on the x-axis and the dependent variable (the variable that you are measuring) is plotting on the y-axis. So assuming that you varied that distance and measured the capacitance (as I imagine you did), then your plot is correct.

    Since (as you correctly say), [itex]C\propto 1/d[/itex] and all of the constants are positive, your gradient will also be positive. Perhaps your instructor misspoke or you misheard.
     
    Last edited: Feb 4, 2008
  4. Feb 4, 2008 #3
    thank you for your help.
     
  5. Mar 31, 2008 #4
    1/D is not intuituve

    I grant you the formula for determining capacitance, but I would think that increasing distance would increase the ability of the plates to hold charge as it would increase the insulation of the dielectric and thus decrease the possibility of short across the dielectric and thus increasing the voltage across the plates. Why is C inversely proportional to distance and not directly proportional?
     
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