**7.4 Elongation**

The strain occurs when stress is given to a film (2 � 2 cm<sup>2</sup> ) sample, which causes it to stretch. Strain is the distortion of a strip before it breaks due to stress. The formula for calculating it is as follows-

$$\% \text{Elongation} = \frac{\text{Increase in length of film}}{\text{Initial length of film}} \times 100 \tag{1}$$
