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Clausius–Mossotti relation

The Clausius–Mossotti relation expresses the dielectric constant (relative permittivity, εr) of a material.

$$\frac {\epsilon _{\mathrm {r} }-1}{\epsilon _{\mathrm {r} }+2}}={\frac {N\alpha }{3\epsilon _{0}}$$

where * ϵr=ϵ/ϵ0\epsilon_{r}=\epsilon /\epsilon _{0} is the dielectric constant of the material * ϵ0\epsilon_{0} is the permittivity of free space * NN is the number density of the molecules (number per cubic meter), and * α\alpha is the molecular polarizability in SI-units (C·m2/V).