A solid ball of radius R has a charge density ρ given by ρ=ρ_o (1- r / R ) for 0 ≤ r ≤ R. The electric field outside the ball is:

A solid ball of radius R has a charge density $\displaystyle \rho$ given by $\displaystyle \rho=\rho_{\mathrm{o}}(1-\mathrm{r} / \mathrm{R})$ for $\displaystyle 0 \leq \mathrm{r} \leq \mathrm{R}$. The electric field outside the ball is :