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 Δ l. Which of the following graphs is a straight line? (a) Δ l versus 1/ l (b) Δ l versus l 2 (c) Δ l versus 1/ l 2 (d) Δ l versus l

Answer: (b). Fixed volume: A = V/l Δ l = Fl/AY = (F l²)/(VY), so Δ l ∝ l² So the graph of Δ l versus l² is a straight line: answer (b).

Copper of fixed volume V is drawn into wire of length l. When this… | NEET 2014 (AIPMT)

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Young's Modulus & Elongation

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 $\Delta l$ . Which of the following graphs is a straight line?

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Answer: (b)

Fixed volume: $A = \frac{V}{l}$
$\Delta l = \frac{Fl}{AY} = \frac{F l^2}{VY}$ , so $\Delta l \propto l^2$
So the graph of $\Delta l$ versus $l^2$ is a straight line: answer (b).

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