The density of mobile electrons in copper metal is 8.4 times 10^28 per cubic meter. Suppose that i = 6.9 times 10^18 electrons/sec drifting through a copper wire (a typical value for a circuit). The diameter of the wire is 3.4mm. What is the drift speed of the electrons? 2.86 times 10^-4 m/s 4.21 times 10^3 m/s 9.05 times 10^6 m/s 7.45 times 10^-4 m/s Solution Here, n = 8.4 *10^28 m^-3 i = 6.9 *10^18 electrons/sec radius , r = 3.4/2 mm r = 1.7 mm drift speed = I/(n * A) drift speed = 6.9 *10^18/(8.4 *10^28 * pi * (0.0017)^2) drift speed = 9.05 *10^-6 m/s the drift speed of the electrons is 9.05 *10^-6 m/s.