Poisson's ratio μ is defined as the ratio of:
Try it first: pick an option, then read the explanation.
Correct answer: D. None of these
Asked in SSC JE 29/01/2018 (Morning)
Detailed Explanation
Read the order of the ratio carefully — exam options often invert it.
Why “None of these” Is Correct
Poisson's ratio is transverse strain ÷ axial strain. Option (a) gives axial ÷ transverse (which is m = 1/μ), and (b), (c) involve shear strain, which has nothing to do with μ. So none of the options is correct.
| 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. axial strain to transverse strain: This is the inverse, 1/μ (Poisson's number m).
- B. axial strain to shear strain: Shear strain is not part of Poisson's ratio.
- C. shear strain to axial strain: Shear strain is not part of Poisson's ratio.
Key Point
μ = lateral ÷ axial; m = axial ÷ lateral = 1/μ.
Key Concepts for Students
- For steel m ≈ 3.3.
- μ cannot exceed 0.5 for isotropic materials.
- Lateral strain has the opposite sign to axial strain.
Practice more: this is question 22 in Stress and Strain MCQs – Part 2. Try the whole set and check every answer instantly.