The document discusses surface tension, highlighting factors that affect it such as temperature, impurities, and the medium in contact. It explains the concept of capillarity and the behavior of liquids like water and mercury in relation to solid surfaces, specifically detailing the angle of contact. Additionally, it contrasts cohesive and adhesive forces, emphasizing their relevance to the phenomenon of surface tension.

1. SURFACE TENSION
SURFACE TENSION

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FACTORS AFFECTING SURFACE TENSION
1)Decreases with increase in liquid temperature and becomes zero at critical temperature.
2)Affected by the presence of impurities
highly soluble----tension increases
sparingly soluble-----tension decreases
3)Depends upon the medium present on the other side of the liquid.
4)Depends only upon the nature of liquid and is independent of the area of free surface.

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Examples

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Intermolecular forces
Cohesive forces
Adhesive force
These forces are different from gravitational forces and do not obey the inverse square law
The maximum distance upto which two molecules attract each other is called molecular range.

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Water wets the glass tube but mercury does not,explain

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Shape of liquid meniscus in a glass tube

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Angle of contact
The angle inside the liquid between the tangent to the solid surface and the tanget to the
Liquid surface at the point of contact is called the angle of contact for that pair of solid
And liquid.

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1)The angle of contact for those liquids which wet the solid is acute.
it is zero for pure water and clean glass , for ordinary water and glass
It is about 8.
2)The liquid which do not wet the solid have obtuse angle of contact .for
mercury and glass the angle of contact is 135 .
3) The angle of contact for water and siiver is 90.

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Work done in stretching a liquid surface :surface energy of a liquid

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CAPILLARITY
WHEN a glass tube open at both ends is partly dipped vertically in a liquid then the liquid rises or falls
In the capillary .
This phenomenon of risingor depressing of liquid in very fine bored tubes is called capillarity.
If the angle of contact for liquid and material of capillary is acute then liquid rises in capillary but if
Angle of contact is obtuse then liquid level falls in the capillary.

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RISE of liquid in an inclined capillary tube

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