The Viscosity Viva Questions and Answers

(i) Define the coefficient of Viscosity.

Ans: It is the tangential force necessary to keep a unit Velocity gradient amid two layers each of unit area.

(ii) What is the unit of coefficient of Viscosity?

Ns m^-2    

(iii). Define fluid.

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

(iv). Give example for fluids?

Ans: Liquids and gases.

(v). Define viscosity.

Ans: Viscosity is a fluid property in which an internal frictional force acts while the fluid is in motion and resist the relative motion.

(vi) What is Stoke's formula?

Ans: F=6πrηv , Where r = radius, η = fluid velocity, v = sphere velocity

(vii) What is meant by Reynold's number?

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

(viii) Give the Newton's equation for viscous force.

Ans: F= -ηA(dvx/dz)

(ix) Define the unit 'poise'

Ans: It is the unit of viscosity in C.G.S system. The unit is in honor of Poiseuille who did important works on viscosity

1 poise = dynes. second/cm²

(x) What is meant by terminal velocity?

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

(xi). What happens to viscosity of a liquid when temperature increases?

Ans: Viscosity decreases

(xii). What happens to viscosity of a liquid when pressure increases?

Ans: Viscosity increases (except water)

(xiii) What is the effect of temperature on viscosity of liquids?

Ans: Viscosity decrease with the increase in temperature.

(xiv) What is the effect of temperature on the viscosity of gases?

Ans: The viscosity of gasses increase with rise in temperature.

(xv) Aim of the viscosity experiment?

Ans: To determine the coefficient of viscosity of a given liquid by measuring the terminal velocity of a given spherical body.

(xvi) Apparatus for the viscosity experiment in lab?

Ans: A tall glass jar of about 1 m long and 2 cm radius, viscous liquid (ex: castor oil or diesel), lead shots or small ball bearings of different size, screw gauge, stop watch etc.