Young's modulus:-
It is defined as the ratio of the linear stress to linear strain, provided the elastic limit is not exceeded. the unit of Y is Nm-2.
Determination of Young's modulus of the material of a wire:-
The apparatus consists of two wires of the same length and equal thickness hung side by side from a rigid support as shown in Fig. The wire A (called the reference wire) carries a millimeter scale S and wire B (called the experimental wire) has a vernier scale V.
When the wire is loaded, that is, it is pulled down by a force, the reaction of the support provides an equal and opposite force. The experimental wire is initially loaded with some weight so as to make it straight and the reading of the vernier is recorded again. The difference between two vernier readings gives the extension produced by the load.
If L is the initial length of the wire and M is the load required to produce an extension ΔL, then
Stress = F/A = Mg/πr2
Where r = radius of the wire
and Strain = ΔL/L
Y = stress/strain = Mg/πr2 . l/ΔL
Knowing M, L, ΔL and r, the value of Y is determined.
