Practice question

Given: A silver sphere of radius 8 cm at 70° C is cooled to 20° C . What is the decrease in its volume? ( α_l = 1.9 × 10⁻⁵K^{-1 ) Formula: Given: r = 8 cm, V_0 = 4/3 π × 8³ = 2048/3 π cm³, Δ T = 20 - 70 = -50° C, α_l = 1.9 × 10⁻⁵K^{-1. Substitution & Calculation: α_v = 3 α_l = 3 × 1.9 × 10⁻⁵= 5.7 × 10⁻⁵K^{-1 . Δ V = V_0 α_v Δ T = 2048/3 π × 5.7 × 10⁻⁵ × (-50) . Δ V = 2048/3 π × (-2.85 × 10⁻³) approx -6.12 π approx -19.22 cm³ (decrease of 19.22 cm³ ). Final Result: The computed value matches expected outcome and confirms correct choice as per latest NCERT 2026-27.