Class 7
Chapter 4 Class 7 - Heat

Conduction

The process through which heat is transferred within an object , when a temperature difference is present between 2 regions of a metal  is known as conduction .

  • In short, transfer of heat from the hot end to the cold end of solid objects is known as conduction .
  • Materials that allow heat to pass through them easily are known as conductors .
    • For example - Copper , Iron (and other metals )
  • Materials that do not allow heat to pass through them easily are known as insulators .
    • For example - Rubber , Wood .
  • Conduction is involved in the transfer of heat from one end of a pan handle to the other end , which turns hot even though there is no flame under it. 

Convection

The process by which heat is transferred in fluids is known as convection .

  • When fluid (water) near the flame is heated, it rises from the bottom and cold water rushes in from the sides to fill in the gap. 
  • As this water also gets heated, more cold water rushes in from the sides to fill in the gap, until heat is dissipated through the entire fluid .
  • This phenomenon is also seen in other fluids such as air .

 

Radiation

The process by which heat is transferred without the presence of a medium (solid or fluid) is known as Radiation .

  • It can take place whether the medium is present or not .
  • All bodies radiate heat. 
    • Some of this radiated heat is absorbed by the surroundings (making it hotter).
    • Some of it is transmitted  (passes) through the surroundings.
    • The rest is reflected by the surfaces it comes into contact with.

For example - 

  • When the pan is taken away from the flame, it transfers heat to the surrounding by radiation .
  • Similarly, the heat from a heater during winters reaches us by radiation .
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CA Maninder Singh is a Chartered Accountant for the past 14 years and a teacher from the past 18 years. He teaches Science, Economics, Accounting and English at Teachoo