Cross sectional area - Young Modulus

[RCB]

out of interest does cross sectional area change when a force is applied (lets say I had a wire and I applied a force to it, the wire would stretch ) does its cross sectional area change

 

[PhanthomJay]

Yes. During the stretching, the volume remains constant, so if the length increases, the area must decrease. Stretching a rubber band provides a good example of this. If the wire is steel, the stretch is relatively small under light loads, and thus the area reduction is small; as the load increases, then so does the elongation, and the reduction in area becomes significant beyond the wire's elastic limit as it approaches it's ultimate breaking strength.