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PRACTICE / Drift velocity

Count carriers crossing the wire

A metal wire carries current 3.2 A through area 1.0 mm². Its mobile-electron number density is 8.0 × 10²⁸ m⁻³. Use electron charge magnitude 1.6 × 10⁻¹⁹ C.

Find the electron drift-speed magnitude.

Organize the givens & assumptions
  • I = 3.2 A
  • A = 1.0 mm²
  • n = 8.0 × 10²⁸ m⁻³
  • |e| = 1.6 × 10⁻¹⁹ C

Uniform density and area, steady current and one carrier type; requested magnitude, not signed direction.

  1. A3.2×106 m/s3.2\times10^6\ \mathrm{m/s}
  2. B2.5×10−4 m/s2.5\times10^{-4}\ \mathrm{m/s}
  3. C2.5×10−10 m/s2.5\times10^{-10}\ \mathrm{m/s}
  4. D2.5×102 m/s2.5\times10^2\ \mathrm{m/s}

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