Calculate the induced dipole moment per unit volume (density of polarization) of He
gas if placed in a field of 6 x 105 V/m. the atomic polarizability of He atom is 2.6 x
1025/m3
. Also calculate the separation of positive and negative charges in each atom.
Answers
Answer:
Total Polarization
In the presence of electronic, ionic and dipolar polarization mechanisms, the average induced dipole moment per molecule pav will be the sum of all the contributions in terms of the local field (effective field) acting on each individual molecule,
Clausius Mossotti Equation | Static relative Permittivity | Polarization of Dielectric Materials equation 1
where αe, αi and αd are the electronic, ionic and dipolar (orientational) polarizabilities. Eloc is the local field, the effective field, at the site of an individual molecule that causes the induced polarization. Each effect adds linearly to the net dipole moment per molecule which is a fact verified by experiments. Interfacial polarization cannot be simply added to the above as αif Eloc because it occurs at interfaces and cannot be put into an average polarization per molecule in the bulk.
Further, the fields are not well defined at the interfaces. In the simplest case (valid for gases), we can take the local field to be the same field (average field in the sample). This means that Eloc = E and therefore polarization Clausius Mossotti Equation | Static relative Permittivity | Polarization of Dielectric Materials equation 2 Since P = Npav, where N is the number of atoms or molecules per unit volume,
Clausius Mossotti Equation | Static relative Permittivity | Polarization of Dielectric Materials equation 3
where α is the polarizability of the molecule. In solids we have to consider the actual effective field acting on a molecule. In the case of electronic and ionic polarization, the local field for cubic crystals and isotropic materials (such as liquids) can be shown to be given by the Lorentz field
Clausius Mossotti Equation | Static relative Permittivity | Polarization of Dielectric Materials equation 4
Explanation:
P=np=nαE
α is the polarisability
E is the electric field
n is the concentration
