A uniform dielectric ball is placed in a uniform electric field of strength $$E_{0}$$. Under these conditions the dielectric becomes polarized uniformly. Find the electric field strength $$E$$ inside the ball and the polarization $$P$$ of the dielectric whose permittivity equals $$\epsilon$$.
By superposition the field $$\vec {E}$$ inside the ball is given by
$$\vec {E} = \vec {E_{0}} - \dfrac {\vec {P}}{3\epsilon_{0}}$$
On the other hand, if the sphere is not too small, the macroscopic equation $$\vec {P} = (\epsilon - 1) \epsilon_{\theta} \vec {E}$$ must hold. Thus,
$$\vec {E} \left (1 + \dfrac {1}{3} (\epsilon - 1)\right ) = \vec {E_{0}}$$ or, $$\vec {E} = \dfrac {3\vec {E_{0}}}{\epsilon + 2}$$
Also $$\vec {P} = 3\epsilon_{0} \dfrac {\epsilon - 1}{\epsilon + 2} \vec {E}_{0}$$.