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Standard IX

Physics

Cohesive Force

explain why a...

Question

explain why angle of contact of mercury with glass is obtuse while water with glass is acute.?

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Solution

The cohesive force between the molecules of mercury is more than the adhesive force between the molecules of mercury and those of glass.This results in the formation of a convex meniscus for the surface of mercury. Actually,cohesive force and Adhesive forces are the phenomenon due to the surface tension of a liquid. The angle made by the mercury from the glass surface is always obtuse.
The adhesive force between the molecules of glass and water is more than the cohesive force between the molecules of water.This results in the formation of a concave meniscus for the surface of water. The angle made by the water from the glass surface is always acute.

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Similar questions

Q. Explain why the angle of contact is acute for kerosene-glass pair and is obtuse for mercury-glass pair.

Explain why

(a) The angle of contact of mercury with glass is obtuse, while that of water with glass is acute.

(b) Water on a clean glass surface tends to spread out while mercury on the same surface tends to form drops. (Put differently, water wets glass while mercury does not.)

(d) Water with detergent dissolved in it should have small angles of contact.

(e) A drop of liquid under no external forces is always spherical in shape

Q. Water rises to a height of

10 c m

in a certain capillary tube. An another identical tube when dipped inmercury the level of mercury is depressed by

3.42 c m

. Density of mercury is

13.6 g / c c

. The angle of contact for water in contact with glass is

0

and mercury in contact with glass is

135^{o}

. The ratio of surface tension of water to that of Hg is

Q. Water rises to a height of

10 cm

in a certain capillary tube. Another identical tube when dipped in mercury, the level of mercury is depressed by

3.42 cm

. Density of mercury is

13.6 {gm/cm}^{3}

. The angle of contact for water in contact with glass is

0^{\circ}

and mercury in contact with glass is

135^{\circ}

. Then the ratio of surface tension of water to that of mercury is:
(use

\frac{0.0342}{\sqrt{2}} = 0.024

)

Q. Water rises up in a glass capillary up to a height of

9.0 c m

, while mercury falls down by

3.4 c m

in the same capillary. Assume angles of contact for water glass and mercury glass

0^{0}

and

135^{0}

respectively. Determine the ratio of surface tension of mercury and water (

c o s 135^{0} = - 0.71

)

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