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. Current I = ε / (R + r) . As external resistance R becomes very large, R + r ≈ R , so I ≈ ε / R , approaching zero as R to ∞ . Applying I = n