Practice question

Given: A copper wire carries 4.5 A with a drift speed of 1.8 × 10⁻⁴ m/s . If n = 8.5 × 10²⁸ m^{-3 and e = 1.6 × 10⁻¹⁹ C, what is the cross-sectional area? These values define the system as per NCERT data. Formula: Drift speed: v_d = I/n e A. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: Rearrange: A = I/n e v_d . Substitute: A = frac4.58.5 × 10²⁸ × 1.6 × 10⁻¹⁹ × 1.8 × 10⁻⁴. Calculate: A = 4.5/2.448 × 10⁵ approx 1.84 × 10⁻⁵ m² . 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.