Meniscus (hydrostatic)

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Concave (A) and convex (B) meniscus

A meniscus (derived from the Greek Μηνίσκος, "Menískos" = crescent moon) is a bulge in the surface of a liquid . It can concave and convex are distinguished menisci (see figure); both go back to the interaction between the liquid and the surface of the adjacent wall:

  • Concave menisci (Fig. A) arise e.g. B. between water and glass. Concave menisci in fine structures lead to capillarity . When reading a scale for measuring the liquid level, these meniscuses are read on the underside .
  • Convex menisci (Fig. B) occur e.g. B. on mercury barometers ; they are read from the top .

Influencing variables

The water surface hits the wall at the wetting angle. There the curvature is maximal and decreases as you approach the water level.

The contact angle of the meniscus surface on the wall is determined by the three interfacial tensions and is also often subject to hysteresis . The curvature in the further course is proportional to the local pressure difference, see Young-Laplace equation . In weightlessness , the curvature between homogeneous phases is constant, so the meniscus is spherical . In a gravitational field , the surface is far from the wall horizontally , wherein the width of the transition from the density difference between the fluids is dependent.

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