Surface Tension

What is Surface Tension?

Surface tension is a phenomenon in which the surface of a liquid acts like a stretched elastic sheet. It results from the cohesive forces between liquid molecules at the surface.

It is defined as the force per unit length acting along the surface of a liquid.

Formula

Surface Tension (T) = Force / Length

SI Unit: N/m (Newton per meter)

CGS Unit: dyne/cm

Causes of Surface Tension

• Cohesive force between molecules.
• Molecules at the surface experience unbalanced inward force.
• This causes the liquid surface to contract and minimize surface area.

Effects of Surface Tension

• Formation of spherical drops of liquids.
• Insects like water striders can walk on water.
• Capillary rise of liquids in thin tubes.
• Needles can float on water despite being denser.

Factors Affecting Surface Tension

• Temperature: Surface tension decreases with increase in temperature.
• Impurities: Can increase or decrease surface tension depending on their nature.
• Surfactants: Substances like detergents reduce surface tension.

Previous Year Questions

• SSC CGL 2019: Surface tension is due to which force?
• Cohesive force between molecules
• RRB JE 2018: Which phenomenon allows insects to walk on water?
• Surface tension
• HSSC JE 2016: Unit of surface tension in SI system?
• N/m

Applications of Surface Tension

• Soaps and detergents reduce surface tension to enhance cleaning.
• Capillary action used in ink pens and plants' water transport.
• Lubricants use surface tension to spread evenly over surfaces.

Conclusion

Surface tension is a vital physical property resulting from cohesive forces. It has practical importance in various natural and technological processes, and plays a significant role in many competitive exam questions.