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Finding amount of graphite in a Pencil

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

    I have some information about a 2H pencil. There is a current of 0.008 amps and 3.8 volts going through the pencil. The length of the pencil was 16cm and the diameter of the core was 2mm. Calculate the percentage of graphite in the pencil.

    2. Relevant equations
    ohms law
    V= I. R


    3. The attempt at a solution
    i calculated the resistance to be 47.5 ohms, using ohms law.
    i then substituted of my known values into the resistivity formula

    A=3.14159E-06 meters squared

    47.5 =(ρ.0.16)/(3.14159E-06 )
    ρ=0.00093266 ohm meters

    Is this correct so far?
    Also what is the resistivity of graphite ??????
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Sep 1, 2011 #2
    You seem to assume there is a linear relationship kg/k = parts graphite, where k is the conductivity of your sample and kg the conductivity of graphite.

    I'm fairly sure this is not the case for a mixture of two materials where the conductivity of the insulating material is small enough to be assumed zero.

    Ask, "are metalic paints conductive?" I don't believe they commonly are, however there are paints containing silver metal, forumated specifically to conduct well.
  4. Sep 1, 2011 #3
    Just don't get pencils with metallic paints... simple

    Just use those plain, boring, brown pencils... :tongue:
  5. Sep 1, 2011 #4
    what must i do to get on the right track?
  6. Sep 2, 2011 #5
    What is the goal of your experimenting?
  7. Sep 3, 2011 #6
    To find the amount of graphite in the pencil
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