I'm really stuck on this one problem: "A small but measurable current of 4.20E-10 A exists in a copper wire whose diameter is 0.02 cm. Calculate the electron drift speed (in meters/second)." Source: Serway and Jewett I know that: I = 4.20E-10 A n = 8960 kg/m^3 q = 1.6E-19 C d = 2E-4 m J = (I/A) = n x q x v Thus, v = I/(n x q x A) What does A stand for and how would I go about finding it? Also, am I converting things correctly and using the proper value for the density? Any help would be greatly appreciated.