Practice question

**Cells combination** series ε_eq = Σ ε_i, r_eq = Σ r_i, parallel for identical cells ε_eq = ε, r_eq = r/n, n number of cells. Maximum current when external R = r_eq, power transfer theorem, explaining why matching resistances maximizes power. Parallel resistance: (1/R_p) = (1/4) + (1/8) + (1/16) = (4 + 2 + 1/16) = (7/16) ⇒ R_p = (16/7) ≈ 2.29 Ω . Total resistance: Rtₒtₐl = 3 + 2.29 = 5.29 Ω . Total current: I = (ε/Rtₒtₐl) = (18/5.29) ≈ 3.4 A . Voltage across parallel: V = I R_p = 3.4 × 2.29 ≈ 7.79 V . Current through