The stress strain graph for a metal wire is shown in the fig. Upto the point E, the wire returns to its original state O along the curve EPO, when it is gradually unloaded. Point B corresponds to the fracture of the wire. (a) Upto what point on the curve is Hooke's law obeyed? (this point some times called proportional limits).

(b) Which point on the curve corresponding to elastic limet or yield point of the wire?
(c ) Indicate teh elastice and plastic regions of the stree-strain graph.
(d) Describe what happens when the wire is loaded upto a stress corresponding to the point A on the graph and then unloaded gradulally. In particular explain the dotted curve.
(e) Wht is peculiar about the protion of the stree- strain graph from C to B? Upto what stress can the wire be subjected with out causing fracture?