Finding amount of graphite in a Pencil

[Manty]

Homework Statement

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.

Homework Equations

ohms law
V= I. R

resistivity
R=(ρ.L)/(A)

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

R=47.5
A=3.14159E-06 meters squared
L=0.16meters

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 ?

 

[Phrak]

You seem to assume there is a linear relationship k_g/k = parts graphite, where k is the conductivity of your sample and k_g 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.

 

[miniradman]

Ask, "are metalic paints conductive?" I don't believe they commonly are, however there are paints containing silver metal, forumated specifically to conduct well.

Just don't get pencils with metallic paints... simple

Just use those plain, boring, brown pencils... :tongue:

 

[Manty]

what must i do to get on the right track?

 

[Phrak]

what must i do to get on the right track?

What is the goal of your experimenting?

 

[Manty]

To find the amount of graphite in the pencil