We determine elements by their properties. One can easily distinguish between elements by the quality they possess. It can be both physical or chemical. Some of the major properties are- malleability, ductility, sonority, lustrous, melting and boiling points, density, reactions with oxygen, water and acids, etc. One of the most important physical property is conductivity.
We can thus define it as the ability of a material to allow heat and electricity to pass through it. It works with both physical movements of electrons and the transfer of energy between the electrons.
Types of Conductivity
It could be through heat, electricity, liquids, air, etc. Its various types are:
Let us see each of the above types in detail:
Electrical Conductivity (EC)
It is just the reciprocal of resistivity. It is the ability of a material to pass an electric current through it. Its SI unit is siemens/meter. In electrical conduction, there is a real movement of electrons towards the positive electrode.
Factors affecting it are:-
a) Length of material – Length is inversely proportional to conductivity. Therefore, with an increase in length, electron collision increases. Thus, it hampers the flow of electricity.
b) Area- With the increase in the area of cross-section, the conductivity of the material also increases. With more space electrons tends to move freely, thus conducting more electricity.
c) Impurities – When we add the impurity to a material its conductivity will decrease. Like, sterling silver is not as good a conductor as the pure silver. That is the reason why alloys have less EC than pure metals.
Every material has its own EC. Silver has the highest conductivity while lead is the least conductive among metals.
Thermal Conductivity (TC)
Heat is the form of energy which gives us the sensation of warmth. Heat flows between two bodies having a temperature difference. This rate of flow of heat is the TC of that material. Heat always flows from the body having a higher temperature to the body having a low temperature.
Factors affecting it are:-
a) Area of cross-section – It is directly proportional to the area of the material. More is the area higher is the heat transfer.
b) Temperature difference – With more temperature difference the rate of flow of heat will be high. You immediately remove your hand when touched with a heated container, why? Because of the temperature difference between your hand and container high. The heat is immediately transferred and you feel the hotness.
c) Length- More is the length less is heat conductivity. A small iron rod is immediately heated compared with the long one.
d) Material – Like in electricity, material play a huge role in TC also. Good conductor of electricity is also the good conductor of heat. Solids are good conductors in comparison to liquids. Gases being the least conductive.
Ionic Conductivity (IC)
It is the tendency of a substance towards the movement of ions from one site to another in an aqueous solution. Some substances like iodine do not conduct electricity in solid-state. Hence, when they are dissociated in aqueous solution their ions start moving freely and conduct electricity.
Higher is the concentration of salt, higher is the conductivity. Thus, salt or added impurities make water a good conductor of electricity.
Applications of Conductivity
- Building materials like concrete are tested with their conductivity to ensure insulated building from heat.
- TC of electronic devices is checked to prevent their failure by overheating.
- The purity of metals like gold, silver, copper etc is checked by their electrical and TC.
- Mercury is preferable over other elements in clinical thermometer because of its higher TC.
Solved Question for You
Q- Does conductivity has any role to play in our weather conditions?
Ans- Yes, the flow of seasonal wind is due to the thermal conductivity of land and sea. In the day time, the land having good conductivity gets heated quickly than the sea. This temperature difference makes the wind to move from sea to land. Similarly, at night, the earth radiates heat quickly and becomes cold. Water being bad radiator remains hot, thus allowing the wind to flow from sea to land.