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The absorption of ink by blotting paper is an example of the capillary action phenomenon. Capillary action is the ability of a liquid to flow in narrow spaces without the assistance of external forces like gravity. It occurs due to the combined effects of adhesion, cohesion, and surface tension.
Blotting paper is a porous material made with numerous tiny interconnected capillaries or microscopic pores. When ink comes in contact with blotting paper:
Adhesion: Ink molecules are attracted to the fibers of the paper.
Cohesion: Ink molecules stick to each other, helping the liquid move upward.
Surface tension: Forces at the liquid surface pull it along the narrow spaces in the paper fibers.
As a result, ink is drawn into the paper spontaneously, even against gravity, until the available pore space is filled. This process quickly removes excess ink from writing surfaces, preventing smudges.
The other options do not explain this phenomenon correctly:
Viscosity of ink: Viscosity describes how thick or resistant a liquid is to flow, but it doesn’t make the ink rise into the paper.
Diffusion: Refers to the spreading of particles from high concentration to low concentration; this is much slower and not the key mechanism here.
Siphon action: Involves liquid flow due to pressure differences in connected tubes, unrelated to blotting paper.
Capillary action is also responsible for many natural and everyday occurrences, such as:
Water moving upward through the stems of plants.
Oil being absorbed by tissues or cloth.
Wicking of liquid fuels in lamps.
Thus, the absorption of ink by blotting paper happens due to capillary action, where liquid rises through tiny pores in the material without any external force, making it an important physical phenomenon observed in daily life.
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