Young's modulus of elasticity

Young's modulus of elasticity (Y) = It is defined as the ratio of normal stress to the longitudinal strain. It is represented by Y and its value is different for different types of materials.

Y = Normal stress / Longitudinal strain ..(1)

If F is applied force and A is area of wire or body,
then Normal stress =  F/A  .....(2)

If L is length of wire and I(small)is increase in length of wire,
then Longitudinal strain = l/L ....(3)

Put equations (2) and (3) in equation (1), 

we get    Y = (F / A)/(l / L)
Or           Y = (FL)/(AI)

SI unit of Y is N / m² or Pascal (Pa). CGS unit of Y is dyne/cm² and
dimensional formula Y = [ML-1 T-2].