Surface Tension
“Surface tension is the property of a liquid that allows it to resist an external force, due to cohesive nature of its molecules.”
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.
Did you know? Mercury forms spherical droplets due to high surface tension!
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.