WHAT IS THERMAL EXPANSION? - (Part 1)

THERMAL EXPANSION 

 THERMAL EXPANSION: Most of the substance solid, liquid, and gasses expand heating and contact on cooling. Their thermal expansion and contractions are usually small and are not noticeable. However, these expansions and constructions are important in our daily life.

        The kinetic energy of the molecules of an object depends on its temperature. The molecules of a solid vibrate with large amplitude at high temperature than at low temperature. Thus, on heating, the amplitude of vibration of the atoms or molecules of an object increases. They push one another farther away as the amplitude of vibration increases. Thermal expansion result an increase in length, breadth and thickness of a substance.

LINEAR THERMAL EXPANSION IN SOLID 

  It has been observed that solids expand on heating and their expansion is nearly uniform over a wide range of temperature. Consider a metal rod of length Lo at certain temperature To. Let its length on heating to a temperature T becomes L. Thus

                Increases in length of the rod = ΔL = L - Lo

                     Increases in temperature         = ΔT = T - To

  It is found that changes in length ΔL of a solid of a solid is directly proportional to its original length Lo, and the changes in temperature ΔT. That is ;

               

                                            ΔL ∝ LoΔT

                                 or

                                            ΔL = α LoΔT ..............................(1)

                                 or

                                           L - Lo =  α LoΔT

                                 or

                                              L  = Lo (1 + αΔT) ...........................(2)

           

      Where α is called coefficient of linear thermal expansion of the substance.

        Know from equation (1), we get

                    

                                               α   =  ΔL / Lo ΔT ...................................(3)

         Thus, we can define the coefficient of linear expansion a α substance as the fractional increase in its length per kelvin rise in temperature.

VOLUME THERMAL EXPANSION 

    The volume of a solid also changes with the change in temperature is called volume thermal expansion or cubical thermal expansion. Consider a solid of initial volume Vo at certain temperature To. On heating the solid to a temperature T, let its volume becomes V, then 

                        Changes in temperature of a solid  ΔT    =   T - To

            And

                        Changes in the volume  ΔV                    =   V - Vo

     Like linear expansion, The changes in the volume ΔV is found to be proportional to its original volume Vo and changes in temperature  ΔT. Thus

                                            ΔV  ∝  VoΔT

                   Or

                                           ΔV   =  βVoΔT ................................... (4)

                                      V - Vo   =  βVoΔT

                                            V    =  Vo (1 + βΔT) .............................(5)

Where β is the temperature coefficient of volume expansion. by using equation (4), we get

                                             β   =  ΔV / VoΔT

 Thus, we can define the temperature coefficient of volume expansion β as the fractional change in its volume per kelvin change in temperature. The coefficient of linear expansion are related by the linear equation:

                                             β  = 3 α .................................... (6)

To be continue reading please go to next page to read more about Thermal expansion.