Which of the following is the unit of kinematic viscosity:
Try it first: pick an option, then read the explanation.
Correct answer: C. Stoke
Asked in SSC JE 4 MARCH 2017 Morning Shift
Detailed Explanation
Viscosity exists in two distinct forms: dynamic viscosity (shear resistance) and kinematic viscosity (diffusive momentum spread). Each has designated units.
Why “Stoke” Is Correct
Stoke is the CGS unit of kinematic viscosity (1 stoke = 1 cm²/s = 10⁻⁴ m²/s).
| Quantity | SI unit | CGS unit | Conversion |
|---|---|---|---|
| Dynamic viscosity μ | Pa·s (N·s/m²) | Poise (P) = dyne·s/cm² | 1 P = 0.1 Pa·s |
| Kinematic viscosity ν = μ/ρ | m²/s | Stoke (St) = cm²/s | 1 St = 10⁻⁴ m²/s |
| Surface tension T | N/m | dyne/cm | 1 dyne/cm = 10⁻³ N/m |
Why the Other Options Are Wrong
- A. Pascal: Pascal is the SI unit of pressure and stress.
- B. Poise: Poise is the CGS unit of dynamic viscosity.
- D. Faraday: Faraday is a unit of electrical charge.
Key Point
Stoke is the unit of kinematic viscosity (1 stoke = 1 cm²/s).
Key Concepts for Students
- Kinematic viscosity ν = μ / ρ.
- SI unit is m²/s; CGS unit is stoke.
- 1 centistoke = 10⁻² stoke = 1 mm²/s.
Practice more: this is question 76 in Properties of Fluid MCQs – Part 6. Try the whole set and check every answer instantly.