MIND GROW Magazine

Properties of Matter – Stage 1 (Page 2)

Stress, Strain & Stress–Strain Curve (JEE Core Concepts)

1. Strain – Measure of Deformation

Strain is the fractional change in dimension produced due to stress.

Important: Strain has no unit and no dimension (pure ratio).

2. Types of Strain

① Longitudinal Strain

Change in length divided by original length.

Longitudinal Strain = ΔL / L

Tensile strain → stretching
Compressive strain → compression

② Volumetric Strain

Change in volume divided by original volume.

Volumetric Strain = ΔV / V

③ Shearing Strain

Angular deformation produced due to tangential force.

Shearing Strain = tanθ ≈ θ (in radians)

3. Hooke’s Law

Within elastic limit, stress is directly proportional to strain.

Stress ∝ Strain

Stress = k × Strain

JEE Point: Hooke’s law is valid only up to the elastic limit.

4. Stress–Strain Curve (Ductile Material)

A graph plotted between stress (Y-axis) and strain (X-axis).

O–A: Linear region (Hooke’s law valid)
A: Proportional limit
B: Elastic limit
C: Yield point
D: Ultimate tensile strength
E: Fracture point

Key Insight: Beyond elastic limit, deformation becomes permanent.

5. Elastic Limit vs Proportional Limit

Proportional Limit	Elastic Limit
Stress ∝ Strain	Body regains original shape
Hooke’s law valid	Hooke’s law may fail
Lower value	Slightly higher value

6. Brittle vs Ductile Materials

Ductile: Steel, copper (large plastic region)
Brittle: Glass, cast iron (fracture quickly)

JEE Favorite: Brittle materials have almost no yield point.

Stage 1 – Page 2 Summary

Strain is deformation per original dimension
Three types of strain
Hooke’s law validity
Stress–strain curve interpretation

Stage 1 – Page 2 Completed ✅
Next: Elastic Moduli (Young’s, Bulk & Shear) – Page 3

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