Practice question

Given: A conductor has a resistivity of 6 × 10⁻⁸Ω m and α = 4 × 10⁻³°C^{-1 at 20° C . What is its resistivity at 90° C ? These values define the system as per NCERT data. Formula: Use: rho_t = rho_0 [1 + α (T - T_0)]. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: Substitute: rho_t = 6 × 10⁻⁸[1 + 4 × 10⁻³(90 - 20)] . Calculate: rho_t = 6 × 10⁻⁸[1 + 0.28] = 6 × 10⁻⁸ × 1.28 = 7.68 × 10⁻⁸Ω m . 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.