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Find the drift velocity of electrons in a copper wire of length 2 m and cross‑sectional area 1.0 mm² carrying a current of 3 A. Given: number density of free electrons in copper n = 8.5×10²⁸ electrons/m³, charge of electron e = 1.6×10⁻¹⁹ C. Step 1: Convert area to m²: 1.0 mm² = 1.0×10⁻⁶ m². Step 2: Use formula v_d = I / (n A e). Step 3: Plug values: v_d = 3 A / (8.5×10²⁸ × 1.0×10⁻⁶ × 1.6×10⁻¹⁹). Step 4: Calculate denominator: 8.5×10²⁸ × 1.0×10⁻⁶ = 8.5×10²². Multiply by 1.6×10⁻¹⁹ gives 1.36×10⁴. Step 5: v_d = 3 / 1.36×10⁴ ≈ 2.2×10⁻⁴ m/s. Answer: The drift velocity is about 2.2×10⁻⁴ metres per second (0.22 mm/s).