Explain the surface tension phenomenon with examples.

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  1. Surface tension is the process of a surface shrinking and minimizing its surface area.
  2. This phenomenon occurs when the liquid in contact tries to occupy the least surface area possible.
  3. The phenomenon of surface tension can be explained by the molecular theory of matter.
  4. There exist cohesive forces of attraction between molecules of the liquid.
  5. Inside the liquid, these forces average out and produce a net-zero effect.

The diagram below shows forces on molecules inside the water surface.

  1. Therefore the surface has a higher potential energy
  2. Hence to attain a stable equilibrium the surface of the liquid behave like a stretched elastic sheet
  3. The formula for surface tension is T=FL , Where T is surface tension, F is force, and L is the length on which force acts.
  4. SI unit of surface tension is Newton/meter.
  5. At liquid-air interfaces, surface tension results from the greater attraction of liquid molecules to each other (due to cohesion) than to the molecules in the air (due to adhesion). The net effect is an inward force at its surface that causes the liquid to behave as if its surface were covered with a stretched elastic membrane. Thus, the surface becomes under tension from the imbalanced forces. These imbalanced forces have the greatest value on the surface compared to the other points in the liquid. Thus, the maximum potential energy is possessed by liquid on its surface.
  6. Eg- The water droplets on leaves look like small bubbles to minimize surface area

  1. Eg - A needle floats on the surface of liquid due to surface tension
  2. Eg- Capillary action in liquids.

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