Practice question

Given: A copper wire of length 2 m and cross-sectional area 2 × 10⁻⁶ m² carries a current of 2 A . If the number density of free electrons in copper is 8.5 × 10²⁸ m^{-3 and e = 1.6 × 10⁻¹⁹ C, what is the drift speed of the electrons? These values define the system as per NCERT data. Formula: Drift speed is given by v_d = I/n e A. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: Given: I = 2 A, n = 8.5 × 10²⁸ m^{-3, e = 1.6 × 10⁻¹⁹ C, A = 2 × 10⁻⁶ m² . Substitute: v_d = frac28.5 × 10²⁸ × 1.6 × 10⁻¹⁹ × 2 × 10⁻⁶. Calculate: v_d = 2/2.72 × 10⁴= 7.35 × 10⁻⁵ m/s . Result: The computed value matches the expected outcome and confirms the correct choice. Units and powers like J kg⁻¹ K⁻¹, m/s², 10⁻⁵ are properly used as per NCERT.