Explain the experimental determination of Young's modulus.

(N/A) typical experimental arrangement to determine the Young's modulus of the material of a wire is shown in the figure.
It consists of two long straight wires of the same length and equal radius suspended side by side from a fixed rigid support.
The wire $A$ (reference wire) carries a millimeter main scale $M$ and a pan to place a weight. The wire $B$ (experimental wire) of uniform area of cross-section also carries a pan in which known weights can be placed.
$A$ vernier scale $V$ is attached to a pointer at the bottom of the experimental wire $B$,and the main scale $M$ is fixed to the reference wire $A$.
The weights placed in the pan exert a downward force and stretch the experimental wire under a tensile stress. The elongation of the wire is measured by the vernier arrangement. The reference wire is used to compensate for any change in length that may occur due to changes in room temperature; any change in the length of the reference wire will be accompanied by an equal change in the experimental wire.
Both the reference and experimental wires are given an initial small load to keep the wires straight,and the vernier reading is noted.
Now,the experimental wire is gradually loaded with more weights to bring it under a tensile stress,and the vernier reading is noted again.
The difference between the two vernier readings gives the elongation produced in the wire.
Let $r$ and $L$ be the initial radius and length of the experimental wire,respectively. Then the area of cross-section of the wire would be $A = \pi r^2$. The Young's modulus $Y$ is given by $Y = \frac{FL}{A \Delta L}$,where $F$ is the applied force $(mg)$ and $\Delta L$ is the elongation.