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List three names by which heat can be transferred from one place to another place?
Thermal energy from a hot body flows to a cold body in the form of heat. This is called as transfer of heat. There are three ways by which the transfer of heat takes place. These are:
QUICK QUIZ
Think of objects around us getting heat or giving out heat.
Ans: (i) Melting of ice cubes. Ice cube gets heat from the surroundings.
(ii) A hot piece of iron radiates heat.
(iii) A black surface absorbs heat.
(iv) The glass of the greenhouse get heat from the sun.
What is meant by conduction?
OR
Describe in terms of molecules and electrons how heat transfer occurs in solids.
Conduction:
The mode of transfer of heat by vibrating atoms and free electrons in solids from hot to cold parts of a body is called conduction of heat.
Explanation:
The handle of metal spoon held in hot water soon gets warm. But in case of a wooden spoon, the handle does not get warm. Both the materials behave differently regarding the transfer of heat. Both metals and non-metals conduct heat. Metal are generally better conductors than non-metals.
Conduction in solids:
Transfer of heat takes place from hot to cold parts in solids:
In solids, atoms and molecules are packed close together. They continue to vibrate about their mean position. When one of its ends is heated then the atoms or molecules present at that end begin to vibrate more rapidly. They also collide with their neighboring atoms or molecules. In doing so, they pass some of their energy to neighboring atoms or molecules during collisions with them with the increase in their vibrations. These atoms or molecules in turn pass on a part of the energy to their neighboring particles. In this way some heat reaches the other parts of the solids. This is a slow process and very small transfer of heat takes place from hot to cold parts in solids.
How does then flow from hot to cold parts in metals so rapidly than non-metals?
Metals have free electrons. These free electrons move with very high velocities within the metal objects. They carry energy at a very fast rate from hot to cold parts of the object as they move. Thus, heat reaches the cold parts of the metal objects from its hot part much more quickly than non-metals.
All metals are good conductors of heat.
Bad conductors or insulators:
The substances through which heat does not conduct easily are called bad conductors or insulators. Wood, cork, cotton, wool, glass, rubber, etc. are bad conductors or insulators
DO YOU KNOW?
Why Styrofoam boxes are used to keep food hot or ice cream cold for a long time? Styrofoam is a bad conductor of heat. It does not allow heat to leave or enter the box easily.
