| Cue / Question | Notes |
|---|---|
| List the 5 key points on the stress-strain curve. | (1) Proportional limit — Hooke's law holds; (2) Elastic limit — max stress with full recovery; (3) Yield point — permanent deformation begins; (4) Ultimate stress — maximum stress before fracture; (5) Breaking point — material fractures. |
| What is the elastic region? | The region before the elastic limit. Deformation is fully reversible upon removing stress. |
| What is the plastic region? | The region between elastic limit and breaking point. Permanent (irreversible) deformation occurs. |
| How is Y related to the curve? | Y = slope of the linear (proportional) region of the stress-strain graph. Steeper slope = higher Young's modulus = stiffer material. |
| Why is strain dimensionless? | It is a ratio of two lengths (/L), so units cancel. This means stress alone carries the unit Pa = N/. |
Summary: The stress-strain curve visually summarises elastic behaviour. The slope of the proportional region gives Young's modulus. Beyond the elastic limit, materials become plastic. NEET commonly tests identification of regions and comparison of moduli for different materials from graph slopes.