A conducting sphere$A$ of radius $a$, with charge$Q$, is placed concentrically inside a conducting shell $B$ of radius $b,$ $B$ is earthed. $C$ is the common center of $A$ and $B,$ then the

field at a distance r from $C,$where $a$$\le r\le b,is\frac{Q}{4\pi {\epsilon }_0{r}^2}$

potential at a distance$r$from $C,$where $a\le r\le b,is\frac{Q}{4\pi {\epsilon }_{0}r}$

potential difference between $A$ and $B$ is $\frac{Q}{4\pi {\epsilon }_0}\left(\frac{1}{a}-\frac{1}{b}\right)$

potential at a distance$r$from $C$, where $a$$\le r\le b,is\frac{Q}{4\pi {\epsilon }_0}\left(\frac{1}{r}-\frac{1}{b}\right)$