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When cells are connected in series, their electromotive forces (emf) may either add or subtract depending on the orientation of their terminals, but their internal resistances always sum up. If opposite terminals of cells are connected, their emf adds, while if like terminals are joined, their emf subtracts. What is the correct expression for the total emf in this case?

1. E₁ / r₁ + E₂ / r₂
2. 18 / 2 + 12 / 1
3. 1 / r₁ + 1 / r₂
4. 1 / 2 + 1 / 1 = 14V

Correct answer: 18 / 2 + 12 / 1

Solution

In a series combination of cells, the total emf is the algebraic sum of individual emfs, and the total internal resistance is the sum of individual resistances. Option B represents the correct calculation of emf and resistance in a series combination.

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