The graphite in a pencil has a resistivity of 7.84×10^?6 W*m. The graphite's diameter is 0.700 mm and its length is 40.0 mm.
(a) Find the resistance of this graphite "wire."
(b) Find the diameter of a cylindrical copper wire of the same length (having resistivity 1.70×10^?8 W*m) that would produce the same resistance.