The number density of free electrons in a copper conductor estimated in Example 3.1 is `8.5 xx 10^28 m^-3`. How long does an electron take to drift from one end of a wire 3.0 m long to its other end? The area of cross-section of the wire is `2.0 xx 10^-6 m^2` and it is carrying a current of 3.0 A.