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**heathrowjohnny** Find the potential inside and outside a uniformly charge sphere of radius $\displaystyle R $ and whose total charge is $\displaystyle q $. Use infinity as your reference point.

So $\displaystyle V(r) = -\int_{\infty}^{r} \bold{E} \cdot d \bold{l} $. What is the electric field inside the sphere?

Then outside the sphere $\displaystyle \bold{E} = \frac{1}{4 \pi \epsilon_{0}} \frac{q}{r^2} \bold{r} $. Then $\displaystyle V(r) = -\int_{\infty}^{r} \bold{E} \cdot d \bold{l} = \frac{q}{4 \pi \epsilon_{0}} \frac{1}{r} $.

For inside the sphere how would you compute the potential?