MCQ
The maximum elongation of a steel wire of $1 \mathrm{~m}$ length if the elastic limit of steel and its Young's modulus, respectively, are $8 \times 10^8 \mathrm{~N} \mathrm{~m}^{-2}$ and $2 \times 10^{11} \mathrm{~N} \mathrm{~m}^{-2}$, is:
  • A
    $0.4 \mathrm{~mm}$
  • B
    $40 \mathrm{~mm}$
  • C
    $8 \mathrm{~mm}$
  • $4 \mathrm{~mm}$

Answer

Correct option: D.
$4 \mathrm{~mm}$
d
In the case for maximum elongation,

Stress $=$ Elastic limit

$\delta_{\text {max }}=\frac{\sigma_{\text {elastlc }} \times L}{\text { Young's modulus }}=\frac{8 \times 10^8 \times 1}{2 \times 10^{11}}  =4 \times 10^{-3}$

$=4 \mathrm{~mm}$

i.e. maximum elongation is $4 \mathrm{~mm}$

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