7th Class Science Heat Transfer of Heat

     Transfer of Heat

Heat is transferred from one medium to another by three ways. These are conduction, convection and radiation. In a solid, heat is transferred from one part to another by the conduction method. In liquid and gases, heat is transferred from one molecule to another by convection method. And in vacuum, where medium is not present, heat is transferred by radiation.

Look at the following picture of heat transfer in solid

In the above picture an iron rod has been heated and heat is transferred from its rounded part to whole part. The rate of transfer of heat depends on the length of the rod and the amount of heat received by the rod from heat producing elements. The other parts of the rod gets heated by conduction. And the rods around the heated rod get heat by radiation.

Look at the following picture of the method of heat transfer from one object to another

In the above picture a pan filled with water is heated by the radiation of heat from a stove. Water, at the lower level of the pan gets heated first because of its closeness with the heat radiating stove. Heated water goes upward and cold water comes down ward. Water inside the pan is heated by convection method. The whole part of the pan is heated by conduction of heat.

       Which one of the following process is involved for heating the liquid inside the pan?

(a) Conduction

(b) Convection

(c) Radiation

(d) All of these

(e) None of these

Answer (b)

      Heating of the Earth by the Sun is an example of:

(a) Conduction method of heat

(b) Convection method of heat

(c) Radiation method of heat

(d) All of these

(e) None of these

Answer: (c)