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National Bird Day is celebrated every year on 5 January . This day is observed to spread awareness about birds, their importance in nature, and the need to protect them. Birds are beautiful living beings and play a very important role in keeping our environment healthy. Origin of National Bird Day National Bird Day was first celebrated in the year 2002 . It was started by bird lovers and environmental groups to protect birds from dangers like deforestation, pollution, and illegal hunting. The main aim of this day is to teach people, especially students, why birds are important and how we can help save them. Why Is National Bird Day Celebrated Every Year? National Bird Day is celebrated every year because many bird species are disappearing due to human activities. Cutting trees, using plastic, pollution, and climate change are harming birds and their homes. This day reminds us that: Birds need protection Nature should be respected Everyone has a responsibil...
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Dulong and Petit's law

Dulong and Petit's law

  • According to Dulong and Petit's law the product of atomic weight and specific heat for all the elements in its solid state is always constant and its value is approximately 6.4. 
  • This law is used to determine the atomic weight of substance.

    Dulong and Petit’s law from Kinetic theory

  • According to the law of equi-partition of energy, the average kinetic energy of translation associated with each degree of freedom is 1/2kT.
  • If the oscillatory motion of atom is simple harmonic then in each oscillation the average kinetic energy = Average potential energy.
        Total energy associated with each degree of freedom of atom 
                                    = 1/2 kT + 1/2 kT = kT
        Since there are three degrees of freedom for oscillatory motion of each atom
        So the total energy of each atom = 3kT
        If we consider the 1 gm-atom of any solid at absolute temperature T
        So the number of atoms in 1 gm-atom of gas = N, where N is Avogadro number
        Total energy of 1 gm of solid
                  U = N * 3 kT = 3NkT                      [ R = Nk ]
                  U = 3RT
                 dU/dT = 3R
        Since dU/dT is the atomic heat of solid at constant volume i.e., Cv            
        So,    Cv = 3R
        Since R = 1.98 cal/gm-atom/°C
        So,    Cv = 3 * 1.98 = 5.94 cal/gm-atom/°C
        Atomic heat of solid = 6 cal cal/gm-atom/°C  (approximate)
       Thus it agrees with Dulong and Petit's law

Failure of Dulong and Petit's law

  • C, B, Si like non-metallic elements have value of atomic heat different from 6.4 at normal temperature (about 6.0).
  • But above 500°C their value tends to about 6.4.
  • At absolute zero temperature the value of atomic heat of all the elements tends to zero.
It is clear from the following figure


        Explanation of Failure of Dulong and Petit's law




To know about this lecture in more detail please visit on https://youtu.be/R_xEBgzUmkQ


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