Viscosity Viva Questions and Answers

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Question-1. What is viscosity in fluid mechanics?

Answer-1: Viscosity is a measure of a fluid's resistance to flow. Viscosity is a fluid property in which an internal frictional force acts while the fluid is in motion and resist the relative motion.

Question-2. How is viscosity typically measured?

Answer-2: Viscosity is measured using a viscometer or viscosimeter.

Question-3. Define the coefficient of viscosity?

Answer-3: It is the tangential force necessary to keep a unit velocity gradient amid two layers each of unit area.

Question-4. What are the SI units of viscosity?

Answer-4: The SI units of viscosity are Pascal-seconds (Pa·s) or N·s/m^{2}.

Question-5. Explain the concept of dynamic viscosity?

Answer-5: Dynamic viscosity measures a fluid's internal resistance to shear forces when it flows. It is represented by the symbol η (eta).

Question-6. Define fluid?

Answer-6: Fluid is a substance which begins to flow when external force is applied on it.

Question-7. Give example for fluids?

Answer-7: Liquids and gases.

Question-8. What is kinematic viscosity, and how is it calculated?

Answer-8: Kinematic viscosity is the ratio of dynamic viscosity (η) to the density (ρ) of a fluid. It is calculated using the formula: ? = η / ρ.

Question-9. Why is it important to measure viscosity in various applications?

Answer-9: Viscosity measurements are crucial for quality control, process optimization, and understanding fluid behavior in industries like manufacturing, pharmaceuticals, and food processing.

Question-10. Name a common instrument used to measure viscosity in a laboratory?

Answer-10: A common instrument is the Ostwald viscometer.

Question-11. What is Stoke's formula?

Answer-11: F=6πrηv , Where r = radius, η = fluid velocity, v = sphere velocity

Question-12. What is meant by Reynold's number?

Answer-12: Rn=(ρVL)/μ , Where ρ = density, V = flow speed, L = linear dimension, μ = dynamic velocity

Question-13. Give the Newton's equation for viscous force?

Answer-13: F= -ηA(dvx/dz)

Question-14. What is the principle behind the capillary tube viscometer?

Answer-14: The capillary tube viscometer measures viscosity by recording the time it takes for a liquid to flow through a narrow tube under gravity.

Question-15. Define shear rate?

Answer-15: Shear rate is the rate at which adjacent layers of fluid move with respect to each other.

Question-16. What is Newton's law of viscosity?

Answer-16: Newton's law of viscosity states that the shear stress in a fluid is directly proportional to the velocity gradient and the dynamic viscosity (η).

Question-17. How does temperature affect the viscosity of most liquids?

Answer-17: Viscosity generally decreases with increasing temperature for most liquids.

Question-18. What is meant by terminal velocity?

Answer-18: Terminal Velocity is defined as the maximum constant velocity attained by a body when falling freely in a viscous medium.

Question-19. Describe the rheological behavior of a Newtonian fluid.

Answer-19: A Newtonian fluid has a constant viscosity regardless of shear rate or stress.

Question-20. What is a non-Newtonian fluid?

Answer-20: A non-Newtonian fluid's viscosity varies with shear rate or stress.

Question-21. Provide an example of a non-Newtonian fluid?

Answer-21: Ketchup is a common example of a non-Newtonian fluid.

Question-22. How is viscosity measured for non-Newtonian fluids?

Answer-22: Non-Newtonian fluids are often characterized using rheometers or rotational viscometers that can vary shear rate.

Question-23. What is the unit of kinematic viscosity in the CGS system?

Answer-23: In the CGS system, kinematic viscosity is expressed in stokes (St).

Question-24. How does the viscosity of gases typically compare to that of liquids?

Answer-24: Gases generally have much lower viscosities than liquids.

Question-25. Explain the concept of absolute viscosity?

Answer-25: Absolute viscosity, also known as dynamic viscosity, quantifies a fluid's internal resistance to shear stress. It is measured in poise (P) in the CGS system.

Question-26. What is the significance of the Reynolds number in fluid dynamics?

Answer-26: The Reynolds number (\(Re\)) is used to predict the flow regime of a fluid and determine whether it is laminar or turbulent.

Question-27. How can viscosity measurements be useful in industries like petroleum or automotive engineering?

Answer-27: Viscosity measurements are crucial for quality control and formulation of lubricants, fuels, and engine oils in industries like petroleum and automotive engineering.

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