Answer
The magnitude of the electric field is $~~\frac{Ze}{4\pi~\epsilon_0}~(\frac{1}{r^2}-\frac{r}{R^3})$
Work Step by Step
We can find the electric field:
$E = \frac{dV}{dr}$
$E = \frac{Ze}{4\pi~\epsilon_0}~(-\frac{1}{r^2}+\frac{r}{R^3})$
When $0 \leq r \leq R,~~$ then $E \lt 0$
The magnitude of the electric field is $~~\frac{Ze}{4\pi~\epsilon_0}~(\frac{1}{r^2}-\frac{r}{R^3})$
