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Karnataka Board PUCPUC Science Class 11

A mild steel wire of length 2L and cross-sectional area A is stretched, well within elastic limit, horizontally between two pillars (Figure). - Physics

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Question

A mild steel wire of length 2L and cross-sectional area A is stretched, well within elastic limit, horizontally between two pillars (Figure). A mass m is suspended from the mid point of the wire. Strain in the wire is ______.

Options

  • `x^2/(2L^2)`

  • `x/L`

  • `x^2/L`

  • `x^2/(2L)`

MCQ
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Solution

A mild steel wire of length 2L and cross-sectional area A is stretched, well within elastic limit, horizontally between two pillars (Figure). A mass m is suspended from the mid point of the wire. Strain in the wire is `underline(x^2/(2L^2))`.

Explanation:

Consider the diagram below


Hence, change in length

ΔL = BO + OC – (BD + DC)

= 2BO – 2BD  .......(∵ BO = OC, BD = DC)

= 2(BO – BD)

= `2[(x^2 + L^2)^(1/2) - L]`

= `2L[(1 + x^2/L^2)^(1/2) - 1]`

= `2L[1 + 1/2 x^2/L^2 - 1]`

= `x^2/L`  ........[∵ x << L]

Strain = `(ΔL)/(2L)`

= `(x^2/L)/(2L)` 

= `x^2/(2L^2)`

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Chapter 9: Mechanical Properties of Solids - Exercises [Page 66]

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NCERT Exemplar Physics [English] Class 11
Chapter 9 Mechanical Properties of Solids
Exercises | Q 9.6 | Page 66

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