Pencil “lead” is actually carbon. What is the resistance of the 0.680 mm-diameter, 4.40 cm-long lead from a mechanical pencil?
RickB was almost correct. You multiply the resistivity by the length and divide by the cross-sectional area. A long, thin resistor will have a greater resistance than a short, wide resistor made of the same material.
Also, different forms of carbon have different resistivity. You’ll want to look up the resistivity of graphite.
Look up the resistivity of carbon in a table.
Multiply by the pencil lead’s cross-sectional area (remember A=πr²).
Divide by the pencil lead’s length.
Resistivity of Carbon (graphite) constant at RT = 3.5e -5
Area = (pi(r^2))
r = (0.680/2/(1000))
pi = 3.14
Resistivity = Res. Constant (σ) * Length (L) / Area (A)
Resistivity = 3.5e -5 * .0440 m / 3.62984e -7 = 4.2426 Ω