# An early model for an atom considered it to have a positively charged point nucleus of charge $Ze$, surrounded by a uniform density of negative charge up to a radius R. The atom as a whole is neutral. For the above model, what is the electrical field at a distance r from the nucleus $(r < R)?$

$(D) \frac{Ze}{4 \pi \in_0^2} \bigg( \frac{1}{r^2} -\frac{r}{R^3}\bigg)$