How to Calculate Stress and Strain in a Spring Experiment

[randomised]

1. we have been using σ=F/A (stress=force/area) and we have done an experement striching a spring and completing a force/extention graph, we have been told to create a stress/strain graph and i couldn't work out how to get the cross sectional area of the spring... and I've been told that there was a deliberate mistake.
please help!?



2. σ=F/A, ε=∆x/l



3.??

 

[mgb_phys]

Normally you would plot force against strain and so the stress would be in arbitrary units of force/sping area.