The journey of an electron through an external circuit involves a long and slow zigzag path that is characterized by losses in electric potential. We now look extensively at resistance - the cause for these voltage drops. Resistivity is defined by the ratio of the magnitude to electric field and current density. Resistance is related to resistivity by R= rhoL/A for cylindrical conductors. Two wires - A and B - with circular cross-sections have identical lengths and are made of the same material. Yet, wire A has four times the resistance of wire B. How many times greater is the diameter of wire B than wire A?