Question

what is the value of angle at contact for convex and concave suntace​

Answer 1

Answer:

A liquid is to be kept in a vessel and thus, liquid is in contact with some solid surface. For a pair of solid and liquid, the angle of contact θ , is defined as the angle between tangent to the liquid surface drawn at the point of contact and the solid surface inside the liquid.

-If the θ<900 , the liquid will have a meniscus concave upwards.

-If the θ>900 , the liquid surface will have a meniscus convex upwards.

-If the θ=900 , the surface of the liquid at the point of contact is plain.

Characteristics of angle of contact:

-It depends upon the nature of the solid in contact and liquid, and is constant for a given liquid-solid pair, other factors remaining unchanged.

-It is independent of the inclination of the solid to the liquid surface.

-It changes with surface tension. As it changes with surface tension the temperature and the purity of the liquid changes with surface tension. It depends upon the medium above the free surface of the liquid.

PROPERTY ANGLE OF CONTACT <900 ANGLE OF CONTACT=900 ANGLE OF CONTACT >900

SUBSTANCE Water and glass Water and silver Mercury and glass

ANGLE OF CONTACT Almost zero.Acute angle Right angle =900 Obtuse angle =1350

MENISCUS SHAPE Concave Plane convex

CAPILLARY ACTION Liquid rises No effect Liquid falls

STICKING TO SOLID Sticks/wets Does not wet Does not wet

RELATION BETWEEN Fa and Fc Fa<FC2–√Fa>Fc Fa=FC2–√ Fa<FC2–√Fa<Fc

SHAPE OF LIQUID SURFACE Almost round Spreads on the surface flat

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