The oil in the wick of an oil lamp rises up due to:

Q. The oil in the wick of an oil lamp rises up due to:

1. gravitational force
2. pressure difference
3. capillary action
4. low viscosity of oil

Answer: Capillary Action

The oil in the wick of an oil lamp rises up due to capillary action. This effect is due to surface tension of liquids. The wick here acts as a capillary tube.

Capillary Action

Adhesion of liquid to the walls of a vessel will cause an upward force on the liquid at the edges and result in a meniscus which turns upward. The surface tension acts to hold the surface intact. Capillary action occurs when the adhesion to the walls is stronger than the cohesive forces between the liquid molecules.
Examples of Capillary Action

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·   Capillary action is essential for the drainage of constantly produced tear fluid from the eye. Two canaliculi of tiny diameter are present in the inner corner of the eyelid, also called the lacrimal ducts; their openings can be seen with the naked eye within the lacrymal sacs when the eyelids are everted.

·   Wicking is the absorption of a liquid by a material in the manner of a candle wick. Paper towels absorb liquid through capillary action, allowing a fluid to be transferred from a surface to the towel. The small pores of a sponge act as small capillaries, causing it to absorb a large amount of fluid. Some textile fabrics are said to use capillary action to "wick" sweat away from the skin. These are often referred to as wicking fabrics, after the capillary properties of candle and lamp wicks.

·   Capillary action is observed in thin layer chromatography, in which a solvent moves vertically up a plate via capillary action. In this case, the pores are gaps between very small particles.

·   Capillary action draws ink to the tips of fountain pen nibs from a reservoir or cartridge inside the pen.

·   With some pairs of materials, such as mercury and glass, the intermolecular forces within the liquid exceed those between the solid and the liquid, so a convex meniscus forms and capillary action works in reverse.

·   In hydrology, capillary action describes the attraction of water molecules to soil particles. Capillary action is responsible for moving groundwater from wet areas of the soil to dry areas. Differences in soil potential drive capillary action in soil.