Ohm's law holds true for a metallic wire only under a specific condition. What is that condition, and why is…

Question

Ohm's law holds true for a metallic wire only under a specific condition. What is that condition, and why is it necessary?

Accepted Answer

## Model Answer The condition is that the **temperature of the metallic wire must remain constant**. This is necessary because resistance depends on temperature. If the temperature rises (due to heating by current), the resistance of the wire changes. Ohm's law states V ∝ I only when resistance R remains constant, which requires constant temperature. *Source: Chapter 11, Section 11.4 – Ohm's Law* --- ## Explanation The examiner expects two things for 2 marks: 1. **The condition** – constant/same temperature (1 mark) 2. **Why it is necessary** – because resistance changes with temperature; V ∝ I holds only if R is constant (1 mark) The textbook phrasing is: *"provided its temperature remains the same"* — use this or paraphrase it closely. Don't just state the law; you must explain the reason to earn full marks.

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