Surface Tension- Fluid Mechanics And Machinery Part-III

Surface Tension One Liner Subjective Questions-Answers from Fluid Mechanics. 

• Surface Tension-The tendency of liquids surface to contracts (shrink) its minimum possible area.
• it is equal to force per unit length
• it is expressed in N/M or dyn/cm (in CGS) and expressed by Sigma 
• dimensional formula of surface tension is MLT 
• the work done to increase per unit area of liquid surface is equal to surface tension and unit is Joule per metre square
• surface tension act in the Plane of the interface normal to any line in the surface 
• when the temperature of liquid increases, the surface tension decreases 
• at critical temperature surface tension is zero 
• the surface tension of Mercury at normal temperature is higher than that of water 
• Mercury does not wet the glass this is due to the properties of surface tension
• A liquid would wet the glass (solid), if the adhesive force more than as Cohesive force
• If cohesion between molecules of fluid is greater than adhesive between fluid and glass then the free level of fluid in a dipped glass tube will be lower than the surface of liquid
• Cohesive force - the acting attractive force between same molecules
• Adhesive force - The acting attractive force between different molecules.
• Cohesion enables it to resist tensile stress
• Effects of surface tension - floating of needle in water, falling drop of water become a sphere, bubbles of soap
• The ratio of inertia force to the surface tension is called - Weber number
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• Capillarity - It is the phenomenon of Rise/Fall of a liquid surface in a small tube when the tube is held vertically in the liquid
• it is expressed in mm or cm of liquid 
• the rise of liquid surface called - capillary rise 
• The Fall of liquid surface called - capillary depression
• capillary rise occurs due to surface tension 
• capillary of liquid depends upon diameter (radius) of capillary tube, surface tension and specific weight 
• rise of liquid in a small diameter tube is more and in higher diameter tube is less
• which liquid wet the glass, this liquid upper the general liquid surface in capillary tube
• which liquid does not wet the glass, this lower the general liquid surface in capillary tube 
• the difference of pressure between the inside and outside of a liquid drop is (P=2T/r)
• if the surface of liquid is convex, then the Cohesion pressure is increased 
• Cohesion between molecules of a fluid is greater than adhesion between fluid and glass, then free level of fluid in a dipped glass tube will be - lower than the surface of liquid.