Practice question

Given: Two lls in parallel have emf 9 V and 3 V with internal resistances 3 Ω and 1 Ω . What is the equivalent internal resistance? These values define the system as per NCERT data. Formula: For parallel: frac1r_{eq = 1/r_1 + 1/r_2 = 1/3 + 1/1 = 1 + 3/3 = 4/3. This is the standard NCERT relation for this phenomenon. Substitution & Calculation: r_{eq = 3/4 = 0.75 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.