Estimate the average drift speed of conduction electrons in a copper wire of cross-sectional area 2.5 × 10⁻⁸ m² carrying a current of 1.8 A. Assume the density of conduction electrons to be 9 × 10²⁸ m⁻³.

The direction of drift velocity of conduction electrons is opposite to the electric field direction, i.e., electrons drift in the direction of increasing potential. The drift speed vd is given by
vd = (I/neA)

Now
e = 1.6 × 10⁻¹⁹ C
A = 2.7 × 10⁻⁸ m²
I = 1.8 A
n = 9 × 10²⁸ m⁻³ (density of conduction electrons)

On substituting values in the formula for vd,
vd = 1.8 A / (9 × 10²⁸ m⁻³ × 1.6 × 10⁻¹⁹ C × 2.7 × 10⁻⁸ m²)
= 5 × 10⁻⁵ m/s = 0.0005 m/s

One gets the final answer as 0.0005 m/s