Practice question

Given: A wire of length 6 m and resistance 15 Ω is stretched to 12 m . What is the new resistance? These values define the system as per NCERT data. Formula: Volume constant: l A = l' A' Rightarrow A' = A/2. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: New resistance: R' = rho l'/A' = fracrho (2l)A/2 = 4 rho l/A = 4R = 4 × 15 = 60 Ω . 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.