A student connects a resistor to a 4 V source and measures a current of 0.5 A. She then doubles the potential…

Question

A student connects a resistor to a 4 V source and measures a current of 0.5 A. She then doubles the potential difference across the same resistor. Predict the new current and justify your answer using Ohm's law.

Accepted Answer

## Model Answer **Step 1: Find resistance using Ohm's law (V = IR)** $$R = \frac{V}{I} = \frac{4	ext{ V}}{0.5	ext{ A}} = 8\ \Omega$$ **Step 2: New potential difference = 2 × 4 = 8 V** Since resistance remains constant (same resistor): $$I_{new} = \frac{V_{new}}{R} = \frac{8	ext{ V}}{8\ \Omega} = \mathbf{1\ A}$$ **Justification:** By Ohm's law, $V \propto I$ (R constant). Doubling the potential difference doubles the current. Source: Chapter 11, Section 11.4 Ohm's Law --- ## Explanation - Examiners expect two clear steps: (1) calculate R from initial values, (2) apply Ohm's law with new V. - Always state the justification explicitly — "V ∝ I when R is constant" is the key Ohm's law statement that earns the second mark. - Don't just give the answer; show the formula and substitution for full credit.

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