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Question:

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 2.7 A. Assume the density of conduction electrons to be 9 × 10²⁸ m⁻³

Solution:

I=neAvd
vd=I/neA
I=2.7 A
e=1.6 × 10⁻¹⁹ C
A=2.5 × 10⁻⁸ m²
n = density of conduction electrons
So, n=9 × 10²⁸ m⁻³
vd=2.7 A/(9 × 10²⁸ m⁻³ × 1.6 × 10⁻¹⁹ C × 2.5 × 10⁻⁸ m²)
=7.5 × 10⁻⁴ A.m/C
=7.5 × 10⁻⁴ m/s