Halliday, Resnick & Walker — Current and Resistance: Problem 26

26 A small but measurable current of \(1.2 \times 10^{-10}\text{ A}\) exists in a copper wire whose diameter is \(3.0\text{ mm}\). The number of charge carriers per unit volume is \(8.49 \times 10^{28}\text{ m}^{-3}\). Assuming the current is uniform, calculate the (a) current density and (b) electron drift speed.