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.