The number density of free electrons in a copper conductor estimated in Example 3.1 is 8.5 × 10²⁸ 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 × 10^–6 m² and it is carrying a current of 3.0 A.

Number density of free electrons in a copper conductor, n = 8.5 × 10²⁸ per meter cube

Length of Copper Wire l = 3 meter

Area of cross section of wire A = 2 × 10^-6 meter square

Current drawn by wire is given 3 Ampere

Since I = nAeV_d

Here V_d is the drift velocity and “e” is the electron charge 1.6 × 10^-19 Coulomb

And V_d Drift velocity is

Therefore

I = nAel/t

Or t = nAel/I

⇒ t = 2.7 × 10⁴ second