Practice question

**Total voltage drop** across series equals source voltage because loop rule Σ V = ε, with internal resistance r included V = ε - I r. For 4 Ω,8 Ω,16 Ω parallel, 1/R_p =1/4+1/8+1/16=7/16, R_p=16/7≈2.29 Ω, then total resistance with internal 3 Ω is 5.29 Ω, current I=18/5.29≈3.4 A. Parallel resistance: (1/R_p) = (1/2) + (1/3) + (1/6) = (3 + 2 + 1/6) = 1 ⇒ R_p = 1 Ω . Total resistance: Rtₒtₐl = 1 + 1 = 2 Ω . Total current: I = (ε/Rtₒtₐl) = (9/2) = 4.5 A . Applying I = n e A v_d, R = ρ l/A,