Poisson's ratio is defined as the:
Try it first: pick an option, then read the explanation.
Correct answer: A. ratio of lateral strain to linear strain
Asked in SSC JE 24/01/2018 (Morning); SSC JE 2011 & 2013
Detailed Explanation
Poisson's ratio is a ratio of strains, not stresses.
Why “ratio of lateral strain to linear strain” Is Correct
It is the ratio of lateral strain to linear (longitudinal) strain, taken as positive. Its value for real isotropic materials lies between 0 and 0.5.
| 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
- B. ratio of linear strain to lateral strain: That is the inverse (Poisson's number m).
- C. ratio of lateral stress to linear stress: Poisson's ratio uses strains, not stresses.
- D. ratio of linear stress to lateral stress: Poisson's ratio uses strains, not stresses.
Key Point
μ = lateral strain / linear strain.
Key Concepts for Students
- In uniaxial loading there is no lateral stress, but there is lateral strain.
- Lateral strain = −μ × longitudinal strain.
- 0 ≤ μ ≤ 0.5.
Practice more: this is question 35 in Stress and Strain MCQs – Part 3. Try the whole set and check every answer instantly.