Use Ohm's law to determine the potential difference across the 3 Ω resistor in the circuit shown in the following diagram when key is closed :
Generated by claude-sonnet-4-6 · 2026-06-15 06:46 · grounding rag
Model Answer
The circuit has resistors 1 Ω, 2 Ω, and 3 Ω connected in series with a 2 V cell.
Step 1: Total resistance
$$R_s = 1 + 2 + 3 = 6 \text{ Ω}$$
Step 2: Current in circuit (Ohm's law)
$$I = \frac{V}{R_s} = \frac{2 \text{ V}}{6 \text{ Ω}} = \frac{1}{3} \text{ A}$$
Step 3: Potential difference across 3 Ω resistor
$$V_3 = I \times R = \frac{1}{3} \times 3 = \textbf{1 V}$$
Source: Chapter 11, Section 11.6.1 – Resistors in Series
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Explanation
- In a series circuit, the same current flows through all resistors (key concept examiners check).
- First find total resistance, then use $I = V/R$ for current, then apply $V = IR$ to the specific resistor.
- Show all three steps clearly — each carries marks. Writing only the final answer risks losing step marks.
- The 1 Ω resistor in the circuit must be included in total resistance calculation; missing it gives wrong current and costs marks.