Finding amount of graphite in a Pencil

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SUMMARY

The discussion focuses on calculating the percentage of graphite in a 2H pencil using electrical properties. The user applied Ohm's Law and the resistivity formula, resulting in a resistance of 47.5 ohms and a calculated resistivity of 0.00093266 ohm meters. The conversation also addresses the misconception regarding the linear relationship between graphite content and conductivity, emphasizing that the conductivity of mixtures does not follow simple proportionality. Additionally, the discussion touches on the conductivity of metallic paints and their implications for experiments.

PREREQUISITES
  • Understanding of Ohm's Law and its application in electrical circuits
  • Familiarity with the concept of resistivity and its formula: R=(ρ.L)/(A)
  • Knowledge of basic geometry for calculating the cross-sectional area of the pencil core
  • Awareness of the properties of graphite and its conductivity
NEXT STEPS
  • Research the resistivity values of different grades of graphite
  • Learn about the relationship between material composition and electrical conductivity
  • Explore the effects of impurities in graphite on its conductivity
  • Investigate the properties of conductive paints and their applications in electrical experiments
USEFUL FOR

Students in physics or materials science, electrical engineers, and anyone interested in the electrical properties of materials, particularly in relation to graphite and its applications in everyday items like pencils.

Manty
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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 ?
 
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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.
 
Phrak said:
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... :-p
 
what must i do to get on the right track?
 
Manty said:
what must i do to get on the right track?

What is the goal of your experimenting?
 
To find the amount of graphite in the pencil
 

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