The graphite in a pencil has a resistivity of7.84×10−6 W×m.The graphite's diameter is 0.700 mm and its length is40.0 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.