Y is defined in terms of longitudinal strain. By definition
Young’s Modulus = Y = normal stress/ longitudinalstrain
Consider a wire of length L, area of cross–section a. A force F is applied to its free end, perpendicular to its area of cross-section. Let ΔL be change (increase) in length of wire. Then
Y is a constant for a meterial. Y does not depend on the dimensions of wire and external applied force. SI Unit of Y is Nm-2 = Pa and its demensions are M-1LT-2 .
