Question

A metal wire is stretched beyond its elastic limit and released, then wire

• A. loses its elastic property completely and it will not contract.
• B. will contract to its original length.
• C. will contract till it achieves its elastic limit.
• D. will contract but its final length will be greater than original length.

Answer 1

The correct option is D will contract but its final length will be greater than original length.

Stress-strain graph of a ductile material is shown in figure.


$OA\to \text{Proportional limit}$
$OB\to \text{Elastic limit}$
$B\to \text{Upper yield stress}C\to \text{Lower yield stress}$
$D\to \text{Ultimate strength}$
$E\to \text{Fracture}$
Point $B$ shows yield point. Material is elastic up to this point $B$. If the material is strained up to point $B$, then on releasing it will regain its original shape

$\Rightarrow$ If material is strained beyond $B$, then it will get deformed permanently, i.e if it is released after straining upto point $B$, it will have an elongation represented by $OQ$.
$\therefore$The material will contract but it won't regain original shape, rather its length will be larger than original.