A fluid, which is incompressible and is having no viscosity is:
Try it first: pick an option, then read the explanation.
Correct answer: C. Ideal fluid
Asked in SSC JE 2014, EVENING
Detailed Explanation
In theoretical fluid dynamics, simplifying assumptions are adopted to formulate governing equations that can be solved analytically.
Why “Ideal fluid” Is Correct
An ideal fluid is defined as having zero viscosity (frictionless) and zero compressibility (constant density, bulk modulus K → ∞).
| Fluid type | Viscosity changes with rate of shear? | Examples |
|---|---|---|
| Ideal fluid | No (μ = 0) | Theoretical only |
| Newtonian fluid | No (μ = const) | Water, air, oil, mercury |
| Non-Newtonian | Yes | Blood, toothpaste, ketchup, paint |
| Ideal plastic (Bingham) | No, but needs yield stress τ₀ first | Fresh concrete, drilling mud |
Why the Other Options Are Wrong
- A. Newtonian fluid: Newtonian fluids have a finite, non-zero dynamic viscosity.
- B. Non Newtonian: Non-Newtonian fluids have finite, shear-dependent viscosities.
- D. Real fluid: All real fluids possess measurable viscosity and compressibility.
Key Point
An ideal fluid is frictionless (no viscosity) and incompressible.
Key Concepts for Students
- Ideal fluid shear stress is always zero: τ = 0.
- Allows the use of Euler's equation and Bernoulli's equation without viscous loss terms.
- Used as a baseline model for aerodynamics outside boundary layers.
Practice more: this is question 72 in Properties of Fluid MCQs – Part 5. Try the whole set and check every answer instantly.