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
21.Whte or shiny surface are poor absorbers and poor radiators of heat
22. Thermos flask is a device in which heat losses due to conduction ,
convection or radiation are minimized.