Halliday, Resnick & Walker — Current and Resistance: Problem 44

44 The (United States) National Electric Code, which sets maximum safe currents for insulated copper wires of various diameters, is given (in part) in the table. (a) Plot the safe current density as a function of diameter. Which wire gauge has the maximum safe current density? (“Gauge” is a way of identifying wire diameters, and \(1 \text{ mil} = 10^{-3} \text{ in.}\)) (b) What is the current density (assumed to be uniform) in 8-gauge wire for a current of 35 A? Gauge 4 6 8 10 12 14 16 18 Diameter, mils 204 162 129 102 81 64 51 40 Safe current, A 70 50 35 25 20 15 6 3