A copper wire of 10^-2 cm² has 10²⁹ electrons per m³ of the wire. If the current through the wire is 20 A, the drift velocity is-

CONCEPT:

• Drift velocity: The average velocity attained by the electrons under the influence of an electric field is termed the drift velocity. 
  • The free electrons are always in a constant random motion in the conductor.
  • When the conductor is connected to a battery, an electric field is generated.
  • When these free electrons are subjected to an electric field, they slowly drift in the direction of the electric field applied, while maintaining the random motion.
  • At this point, the net velocity of the electrons is called its drift velocity.

The drift velocity (vd) of the electron in a conductor is given by:

 \(v_d =\frac{I}{nAq}\)

Where I is the current flowing through the conductor, A is the area of cross-section of the conductor, q is the charge on the electron and n is the number of electrons.

CALCULATION:

Given that:

Current, I = 20 A

Cross-sectional area of conductor, A = 10-2 cm2 = 10^-6 m²

Density of electrons in the wire, n = 1029 electrons per m3 

\(⇒ v_d= \frac{20}{(10^{29})\;×\;(10^{-6})\;×\;(1.6\;×\;10^{-19})}\)

⇒ v_d = 1.25 × 10^-3 m/s