# Surface Tension and Viscosity Viva Questions

Surface Tension and Viscosity Experiment

The surface tension (capillary rise) Viva Questions and Answers

(i) Define surface tension

Ans: It is defined as the force acting tangential to the liquid surface and perpendicular to unit length of an imaginary line drawn on the surface of the liquid

(ii) What is the unit and dimension of S.T?

Ans: Unit-Nm-1; Dimension MLT-1

(iii) How is surface tension related to surface energy?

Ans: They are the same.

(iv) What is the difference between adhesive and cohesive forces?

Ans: Attraction between molecules of the same kind-cohesive. Attraction between molecules of different kind-adhesive.

(v) What is angle of contact?

Ans: The angle between the tangent to the liquid surface at the point of contact and the solid inside the liquid.

(vi) What is meant by capillarity?

Ans: Rise of liquid in capillary tube is called capillarity

(vii) For mercury there is capillary depression. Why?

Ans: Angle of contact is oblige (140 °)

(viii) What are the factors on which capillary ascent depends?

Ans: Inversely proportion to the radius, inversely proportional to density and directly proportional to surface tension.

(ix) If the angle of contact were 90°. What is capillary accent?

Ans: Zero

(x) Is surface tension is a molecular phenomenon or atomic

Ans: Molecular phenomena.

(xi). What is a capillary?

Ans: A tube with fine bore.

(xii). What is the unit of surface tension?

Ans: N/m

(xiii). Give the value of surface tension of water?

Ans: It is 72.7 x 10-3 N/m at 20° C

(xiv). Define capillary rise.

Ans: Rising of a liquid in a capillary tube is called capillary rise.

(xv). Why doesn't mercury rise in the capillary tube?

Ans: For mercury and clean glass, the angle of contact is obuse. Hence mercury does net rise in the capillary tube.

(xvi). Why does water rise in the capillary tube?

Ans: For water and clean glass, the angle of contact is acute. Hence water rises in the capillary tube.

(xvii). How does surface tension vary with temperature?

Ans: Surface tension decreases with increase in temperature.

(xvii) Aim of surface tension experiment?

Ans: To find the surface tension of water by capillary rise.

(xix) Apparatus for the Surface tension experiment?

Ans: A narrow capillary tube of uniform bore of known radius, beaker containing water, travelling microscope and so on.

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). Define fluid.

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

(iii). Give example for fluids?

Ans: Liquids and gases.

(iv). 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.

(v) What is Stoke's formula?

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

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

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

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

Ans: F= -ηA(dvx/dz)

(viii) 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

(ix) 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.

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

Ans: Viscosity decreases

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

Ans: Viscosity increases (except water)

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

Ans: Viscosity decrease with the increase in temperature.

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

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

(xiv) 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.

(xv) 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.