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A steel wire of length $L$ and cross-section $A$ is stretched by a force $F$, producing extension $\Delta L$. If the length is doubled to $2L$ but $A$ and $F$ are unchanged, the new extension is
A$\Delta L / 2$
B$\Delta L$
C$2\Delta L$
D$4\Delta L$
Answer & Solution
Correct answer: C. $2\Delta L$
From $Y = \dfrac{FL}{A\Delta L}$, holding $Y, F, A$ fixed gives $\Delta L \propto L$. Doubling the length doubles the extension.
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