Wednesday, August 24, 2011

Law of Equipartition of Energy

                   This Law states, "The total energy of a molecule is shared equally by the various degrees of freedom possessed by it."
                     In case of mono atomic molecules like argon and helium, the energy possessed by them is only that of transnational type, the rotational energy being negligible. We have already discussed in Art.
                              Energy of translation per molecule = 3/2*kT
                             Energy per molecule per degree freedom = 1/3*3/2kT

Degrees of Freedom

                         In order to describe completely the motion of a particle in one plane, only two quantities must be known, say its two rectangular components. Similarly, for a particle moving in space, three independent quantities must be known to describe its motion. A molecule in a rigid body can have three motions of vibration along any of three co-ordinates axis in addition to its three motions of translation. It is thus obvious that in order to completely describe the state of motion of a particle, six independent quantities must be known.
                       In general, the total number of independent quantities, which must be known for describing completely the state of motion of a body, are called its degrees of freedom.