c
\(\mathrm{q}=1\, \mu \mathrm{C}=1 \times 10^{-6} \,\mathrm{C}\)

\(r=4\, \mathrm{cm}=4 \times 10^{-2}\, \mathrm{m}\)

\( \text { Potential } V =\frac{\mathrm{k} q}{\mathrm{r}} \)

\(=\frac{9 \times 10^{9} \times 10^{-6}}{4 \times 10^{-2}} \)

\(=2.25 \times 10^{5}\, \mathrm{V} \)

Induced electric field \(\mathrm{E}=-\frac{\mathrm{kq}}{\mathrm{r}^{2}}\)

\(=\frac{9 \times 10^{9} \times 1 \times 10^{-6}}{16 \times 10^{-4}}=-5.625\, \times 10^{6}\, \mathrm{V} / \mathrm{m}\)