Science (086) — AI-generated practice question

Normally, both cells (each 1.5 V) add up in series to give a total EMF of 3 V, producing a current of $I = \frac{3}{5} = 0.6$ A through the bulb.

When one cell is reversed, it opposes the other. The net EMF = 1.5 V − 1.5 V = 0 V. By Ohm's law, $I = \frac{V}{R} = \frac{0}{5} = 0$ A.

The bulb goes out completely — no current flows.

This is consistent with series-circuit principles: in a series circuit the same current flows throughout, and the total potential difference equals the algebraic sum of all individual EMFs. With equal and opposing cells, they cancel, leaving zero net driving voltage and hence zero current.

Source: Chapter 11 – Electricity, Section 11.6.1 Resistors in Series

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• The key series principle here is that EMFs in series add algebraically — a reversed cell subtracts.
• Examiners expect the numerical calculation ($I = V/R$) showing zero current, plus the reasoning using series-circuit rules.
• Do not just say "current decreases" — two identical cells reversed give exactly zero net EMF and zero current, not merely a reduced current.