Interfacial or surface tension exists when two phases are present. SURFACE TENSION When a small quantity of water is poured on a clean glass plate, it spreads in all directions in the form of a thin film. In the case of interface the molecules at the interface will be pulled by both faces into the bulk … Surface tension of a liquid is defined as the force acting at right angles to the surface along 1 cm length of the surface. A highly soluble substance like salt increases the surface tension whereas sparingly soluble substances like soap decreases the surface tension. When dust particles or oil spreads over the surface of water, its surface tension decreases. If angle of contact is obtuse angle, ie; θ > 90°, then liquid will not wet the surface. then radius of each droplet, r = R. (n)-1/3 Surface tension is a phenomenon in which the surface of a liquid, where the liquid is in contact with a gas, acts as a thin elastic sheet. For mercury and glass is 140°. Angle of contact for pure water and glass is zero. Dronstudy provides free comprehensive chapterwise class 11 physics notes with proper images & diagram. If θ is acute angle, i.e; θ <90°, then liquid meniscus will be concave upwards. (i) Excess pressure inside a liquid drop = 2S / R, (ii) Excess pressure inside an air bubble in a liquid = 2S / R, (iii) Excess pressure inside a soap bubble = 4S / R. where, S = surface tension and R = radius of drop/bubble. The water given to the fields rises in the innumerable capillaries formed in the stems of plants and trees and reaches the leaves. Important … The shape of the drop hanging from a needle is determined from the balance of forces which include the surface tension of the liquid being investigated. Water striders stay atop liquid surface due to surface tension 9. Compared to Viscosity, Surface Tension is a simpler phenomenon. The surface tension between gas and crude oil ranges from near zero to approximately 34 dynes/cm. Oxygen in the atmosphere is known to decrease the surface tension of various substances. If θ > 90°, cos 9 is negative, so h is negative, i.e., liquid falls in a capillary tube. Factors affecting surface tension . This work done is stored in liquid stu-face as potential energy. 10.5 Factors Affecting Surface Tension. e.g., the force of attraction acting between molecules of water, glass, etc. The liquid film exerts a force on the movable wire in an attempt to reduce its surface … Angle of contact depends upon the nature of the liquid and solid contact and the medium which exists above the free surface of liquid. The unbalanced … At boiling point, surface tension of a liquid becomes zero becomes maximum at freezing point. NCERT Books. IARCS Olympiads: Indian Association for Research in Computing Science, CBSE 12 Class Compartment Result 2020 (Out) – Check at cbseresults.nic.in, CBSE Class 10 Result 2020 (Out) – Check CBSE 10th Result at cbseresults.nic.in, cbse.nic.in, Breaking: CBSE Exam to be conducted only for Main Subjects, CBSE Class 11 Physics Notes : Thermometry and Calorimetry. (vii) When two soap bubbles of radii ‘1 and ‘2 are in contact with each other, then radius (r) of common interface. The surface tension of liquid is zero at its boiling point and it vanishes at critical temperature. JEE Main & Advanced Physics Fluid Mechanics, Surface Tension & Viscosity Factors Affecting Surface Tension Key points of Factors affecting surface tension: Let’s consider the effects of these four conditions on surface tension: As temperature decreases, surface tension increases. where. Formally, surface tension is defined in much the same way as pressure was defined in equation (2.10) on page 24. Surface tension of the liquid is measured as the force acting per length on an imaginary line drawn tangentially on the free liquid surface the liquid. The property of surface tension is revealed, for example, by the ability of some objects to float on the surface of the water, even though they are denser than water. Interfacial tension is the force that holds the surface of a particular phase together and is normally measured in dynes/cm. 2 Interface is the boundary between two or more phases exist together The properties of the molecules forming the interface are different from those in the bulk that these molecules are forming an interfacial phase. Experimentally it has been found that the surface tension decreases almost linearly with temperature (see surface tension of water as a function of temperature in figure 2). Angle, i.e ; θ < 90°, then due to cohesive force and root of... 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