Energy stored in the wire

Whenever a force is applied on a body  it produces a change  in the shape of the body but due to the elastic nature,the particles tries to come back to their original position. As no body is perfectly elastic there will be a permanent change in the shape of the body which is called as extension or elongation. For producing this elongation we must have done some work and after the job was done, this work and cannot disappear all of a sudden. That is against the law conservation of energy.

This work done hence stored in the format of energy and that is called the energy stored in your wire. It depends on the applied force as well as the extension. Here for producing a small elongation, with respect to the applied force the corresponding work done is also small. The total elongation is the sum of all this kind of small elongation is and the total work done is the sum of all the works done together. To calculate the total amount of the work done therefore we have to add all that works together and that kind of adding is mathematically called integration. In the following diagram we have shown how to derive the equation for the work done.



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Experimental determination of Youngs modulus of the wire

To determine the modulus of elasticity we shall conduct the experiment. The experiment consists of two identical wires suspended from a rigid support.

Among the two wires one wire is a reference wire and the 2nd wire is an actual experimental wire. On the reference wire a fixed weight  is applied whereas on the experimental wire a variable weight  is applied.

A is arranged as shown in the diagram. Initially the apparatus is adjusted to a basic reading. When the load is increased , the reading of the vernier  calipers changes and basing on its concept we can calculate the increase in its length. Once if you know the increase in the length of the wire exactly calculating Young's modulus is very easy as shown below.