Thursday, 14 August 2014

IMPORTANT POINTS TO REMEMBER ON HEAT ICSE


IMPORTANT POINTS TO REMEMBER ON HEAT

1.The expansion produced in matter due to the absorption of heat       
  energy is called Thermal expansion.

2.All states of matter expand on heating.However,solids expand least ,
   the liquids more and the gases most for the same rise in temperature.

3.The expansion in only the length of a solid is called linear expansion.

4.The expansion in the area of a solid is called Superficial expansion.

5.The expansion in the volume of a solid is called cubical expansion.

6.The liquids and gases have only cubical expansion, but no linear or
    Superficial expansion as they have no definite shape.

7.A bimetallic strip consists of two plates of different metals which are
   riveted together at a number of points in such a way that they cannot
  slide on being heated or cooled.

8.The process due to which a solid state changes into liquid state by  
  gaining heat energy is called Fusion or melting and the temperature at  
  which it happens is called Melting Point.

9.The Process due to which a liquid changes into solid state by losing
  heat is called Solidification or Freezing and the temperature at which it  
  happens is called Freezing Point.

10.The process due to which a liquid changes into gaseous state by
    gaining heat is called Boiling or Vaporisation and the temperature at   
   which it happens is called Boiling Point.

11.The Process due to which a gas changes into Liquid state by loosing   
  heat is called Liquefactiom or Condensation and the temperature at 
   which it happens is called  Condensation Point.

12.The process due to which a Liquid changes into its gaseous state
   (Vapours), below its boiling point is called evaporation.

13.The Process due to which a solid directly changes into gaseous state
   On heating and the gaseous state directly changes into solid state on
   Cooling, without changing into liquid state, is called sublimation.
14. Heat is transmitted from a Hot body to a Cold body by the process
  of : (i) Conduction,(ii) Convection, and (iii) Radiation

15. In Conduction, the molecules pass on heat energy to neighboring
      molecules , without actually moving from their positions.

16. Conduction is only possible in solids, with the exception of Mercury
      Which is a liquid.

17.Substances which allow the heat energy to flow through them easily 
   are called Good Conductors, Whereas those which donot allow the
   heat energy to flow through them easily are Bad Conductors.

18.Convection is a process of Heat transfer when molecules actually
   come to the source of Heat and then after absorbing heat energy
   move away from it.

19.Radiation is a mode of transference of heat directly from a hot body
   to cold body without heating the space in between two bodies.

20.Black or dull surfaces are good absorbers and good radiators of heat
   Energy

21.Whte or shiny surface are poor absorbers and poor radiators of heat  
   energy.

22. Thermos flask is a device in which heat losses due to conduction ,
    convection or radiation are minimized.