For an isotropic homogeneous body, the ratio of lateral strain to axial strain is called:
Try it first: pick an option, then read the explanation.
Correct answer: C. Poisson's ratio
Asked in SSC JE 15/11/2022 (Shift 1)
Detailed Explanation
When a body is loaded axially, it deforms both along and across the load.
Why “Poisson's ratio” Is Correct
The ratio of lateral strain to axial (longitudinal) strain (taken as positive) is Poisson's ratio, μ. It is a material constant within the elastic range.
| Material | Poisson's ratio μ |
|---|---|
| Cork | ≈ 0 |
| Concrete | 0.15 – 0.20 |
| Cast iron | 0.21 – 0.26 |
| Steel | 0.27 – 0.30 |
| Copper | ≈ 0.33 |
| Rubber | 0.45 – 0.50 |
For isotropic materials μ cannot exceed 0.5; above that the volume would decrease under tension.
Why the Other Options Are Wrong
- A. modulus of elasticity: Modulus of elasticity is stress ÷ strain.
- B. yield value: Yield value is a stress level, not a strain ratio.
- D. plasticity index: Plasticity index is a soil property (LL − PL).
Key Point
μ = lateral strain ÷ axial strain.
Key Concepts for Students
- μ does not depend on the member's dimensions.
- Metals: 0.25–0.35.
- Rubber ≈ 0.5 (nearly incompressible).
Practice more: this is question 7 in Stress and Strain MCQs – Part 1. Try the whole set and check every answer instantly.