The number density of free electrons in copper is 8 × 10²⁸ m⁻³. A copper wire has cross-sectional area 2 × 10⁻⁶ m² and carries 3.2 A. The drift speed is ______ × 10⁻⁶ m s⁻¹.
Physics · Circular Motion
JEE Mains 8 April 2023 Shift 2 Evening Shift

Question

The number density of free electrons in copper is 8 × 10²⁸ m⁻³. A copper wire has cross-sectional area 2 × 10⁻⁶ m² and carries 3.2 A. The drift speed is ______ × 10⁻⁶ m s⁻¹.

G1 Physics · Accepted Answer

Drift speed is v(d) = I/(neA) Given: I = 3.2 A n = 8×10²⁸ m⁻³ e = 1.6×10⁻¹⁹ C A = 2×10⁻⁶ m² Therefore, v(d) = 3.2 / [(8×10²⁸)(1.6×10⁻¹⁹)(2×10⁻⁶)] = 1.25×10⁻⁴ m s⁻¹ = 125×10⁻⁶ m s⁻¹ Final value: 125