Polarizability $(\alpha) $ –

When the strength of electric field $E$ is increased, the strength of the induced dipole $\mu$ also increases. Thus the induced dipole moment is proportional to the intensity of electric field. Thus, $\mu=\alpha E$ where $\alpha$, the constant of proportionality This is called polarizability. The different types of polarization are – 1)  Electronic polarization 2)  Ionic polarization 3)  Orientation polarization 4)  Space-charge polarization *Electronic polarization –* The displacement of positively charged nucleus & the negative electrons of an atom in opposite direction an application of electric field, results in electronic polarization. On applying the field, the electrons cloud around the nucleus readily shifts towards the positive end of field. As the nucleus & the center of the electron cloud are sperated by certain distance, dipole moment is created within each atom. This shift is proportional to field strength. Since the dipole moment is product of charge & the shift distance, the dipole moment is also proportional to the field strength. Thus, induced dipole moment $\mu\propto E$ or $\mu=\alpha_eE$ where $\alpha_e$ is electronic polarizability it is independent of temperature. It can be proved that – $\alpha _{e} =\dfrac {\epsilon_{o} (E_{r}-1)}{N}$ where $N=$ No. of atoms/unit volume.