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Copper of fixed volume ‘V’, is drawn into wire of length ‘l’. When this wire is subjected to a constant force ‘F’, the extension produced in the wire is ‘Δl’. Which of the following graphs is a straight line?

1. Δl versus 1 / l
2. Δl versus l²
3. Δl versus 1 / l²
4. Δl versus l

Correct answer: Δl versus 1 / l²

Solution

The extension Δl in the wire is inversely proportional to the square of its length (l²) for a constant volume and force, as per the relation Δl ∝ 1/l². Thus, the graph of Δl versus 1/l² will be a straight line.

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