Asked by ruth

a student connects the ends of a pencil lead to a 6.0V supply and measures the current to be 8.6A.the lead is rod of graphite of length 7.5 cm and diameter 1.4mm.
a)calculate the resistance of the pencil
b)use this data to calculate the resistivity of graphite
Answered by Steve
R = E/I = 6/8.6 = 0.70 ohms

Now use the definition of resistivity to work it out.