When a wire is stretched within its elastic limits, work is done on it. This work stores in the wire as the elastic strain energy of the wire.

**Explanation**

Consider a wire of length ‘l’ suspended from one end and to the other end, hang some weight as shown in the fig.

An extension occurs in the length of the wire, which increases as we increase the hung weight.

Let’s calculate the work done on the wire during an extension segment of e.

Let the force F varies from 0 at the start to F at the end for this extension. Then the average force during this interval is = ½ (0+F) = ½ F. As the extension is ‘e’, therefore, the work done is

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