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.