Class 11 Physics Kinetic Theory Translational degree of freedom

Translational degree of freedom:-

  • Translation means motion of the body as a whole from one point to another.
  • For example:
    • Consider the oxygen molecule;it has 2 oxygen atoms which are bonded together.
    • The 2 oxygen atoms along with the bond are considered as whole body.
    • When the body as a whole is moving from one point to another is known as translational.
    • Consider a molecule which is free to move in space and so it will need 3 coordinates(x, y, z) to specify its location.
    • Therefore it has 3 degrees of freedom.
    • Similarly a molecule which is free to move in a plane which is 2 dimensional and so it needs 2 coordinates to specify its location.
    • Therefore it has 2 degrees of freedom.
    • Similarly a molecule which is free to move in line it needs 1 coordinate to specify its location.
    • Therefore it has 1 degree of freedom.
  • Molecules of monoatomic gas have only translational degrees of freedom.This means gases which have only one atom.
  • For example:-Helium atom it consists of only one He atom.It will have translationaldegrees of freedom.
  • Each translational degree of freedom contributes a term that contains square of some variable of motion.
    • The variable of motion means the velocity (vx,vy,vz).
    • The term (1/2) mvx2 will contribute to energy.This is Kinetic energy which is involved with the motion of the molecule from one point to another.

In thermal equilibrium, the average of each such term is (1/2) kBT.

 

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