Practice question

**Electrical power** P = V I = I² R = V²/R (W), energy E = P t = I² R t (J), heating effect Joule's law H = I² R t. When internal r equals external R, total resistance 2R, I = ε/2R, power in external = I²R = ε²/4R, total = ε²/2R, fraction external = 1/2, illustrating maximum power transfer when R = r. Total resistance: Rtₒtₐl = 4.5 + 0.5 = 5 Ω . Current: I = (ε/Rtₒtₐl) = (5/5) = 1 A . Power: P = I² R = 1² × 4.5 = 4.5 W . Applying I = n e A