A chemical cell of electromotive force (emf) 1.50 V and internal resistance 0.50 Ω is connected across an external resistor of 2.50 Ω. Calculate the terminal potential difference across the cell.

Answer and explanation

Correct answer: A. 1.25 V

  1. Step 1: Calculate total resistance: R_total = R + r = 2.50 + 0.50 = 3.00 Ω. Step 2. Compute circuit current: I = E / R_total = 1.50 / 3.00 = 0.50 A. Step 3. Calculate terminal pd: V = I R = 0.50 × 2.50 = 1.25 V. (Alternatively V = E - Ir = 1.50 - 0.25 = 1.25 V). Answer: 1.25 V. Why not the others: 1.50 V is the open-circuit emf; 0.25 V is the lost voltage inside the cell (Ir); 1.00 V is an arbitrary guess.

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