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Monday, 28 September 2015

FSc Notes Chemistry Part 1 Chapter 4 Liquids and Solids Lecture 5



FSc Notes Chemistry Part 1 Chapter 4 Liquids and Solids Lecture 5


Capillary Action:

“The rise of a liquid in a capillary tube is known as capillary action”. A capillary tube is a thin glass tube with a small opening. In case of liquids whose cohesive force are weak and adhesive forces are stronger have the ability to attach with the wall of capillary tube and can rise in it. Such liquids are called wetting liquids. Water is a best example such liquids show capillary action. On the other hand liquids which have strong cohesive and weak adhesive forces do not show capillary action because their molecules do not stick to the walls of capillary tube. Such liquids are known as non-wetting liquids. Best example is mercury (Hg).

Liquid Crystal:

The substances which are like semi solids and have properties of both liquid and solids are known as liquid crystals.
Such substances are semi-solids as well as semi-liquids because they have properties of both liquids and sold (crystalline) substances.
Liquid crystals show optical properties which are the characteristics of crystalline solids. Similarly liquid crystals show that the properties like surface tension and viscosity which are the characteristics of liquids.

Similarly a crystalline solid is anisotropic but liquid crystals are isotropic.
If a solid is heated, then just near to its melting point it converts into a turbid shape or as a suspension i.e. a liquid containing heated further then we get a clear liquid. This turbid form of the substance may be termed as liquid crystal.

Uses of Liquid Crystal:

Liquid crystals have got so many important applications. Many of the organic compounds and biological tissues behave as liquid crystals.
Some important applications of liquid crystal are.

  1. Liquid crystals are used as temperature sensors. They get different color at different temperatures due to diffraction of light falling upon them.
  2. Liquid crystals can also be used to find the point potential of failure in electrical circuits.
  3. Liquid crystals are used as solvent in chromatography.
  4. liquid crystal screens are used in oscillographs ant TV display.
  5. Room thermometers have liquid crystal with a particular temp range. As the temp changes figures show up in different colors.
  6. liquid crystalline substance are used to locate the veins arteries, infections and tumors. The infected areas of the body are warmer than other areas. Thus when liquid crystalline substance touch the infected areas their color is changed and thus the infection is detected. The specialists can use the technique of skin thermograph to detect blockage in veins and arteries.

Written by: Asad Hussain

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