Consider two large parallel conducting plates placed close to each other. It is observed that the inner surfaces of the two plates have surface charge densities $+\sigma$ and $-\sigma$ whereas the outer surfaces posses no charge. If $\overrightarrow{E}$ be the electric field between the plates of the capacitor then in the region

$$\begin{gathered} \mathrm{Electric} \mathrm{field} \mathrm{due} \mathrm{to} \mathrm{the} \mathrm{single} \mathrm{plate} \mathrm{is} \frac{\mathrm{\sigma }}{2{\mathrm{\epsilon }}_0} \mathrm{for} \mathrm{positive} \mathrm{plate} \\ \mathrm{its} \mathrm{direction} \mathrm{will} \mathrm{be} \mathrm{away} \mathrm{from} \mathrm{the} \mathrm{plate} \mathrm{for} \mathrm{positive} \mathrm{plate} \\ \mathrm{and} \mathrm{for} \mathrm{negative} \mathrm{plate} \mathrm{it} \mathrm{is} \mathrm{towards} \mathrm{the} \mathrm{plate}. \\ \mathrm{so} \mathrm{in} \mathrm{between} \mathrm{the} \mathrm{plates} \mathrm{they} \mathrm{are} \mathrm{in} \mathrm{the} \mathrm{same} \\ \mathrm{direction} \mathrm{towards} \mathrm{the} \mathrm{negative} \mathrm{plate}. \\ \mathrm{Hence} \mathrm{net} \mathrm{electric} \mathrm{field} \mathrm{is} \frac{\mathrm{\sigma }}{2{\mathrm{\epsilon }}_0}+\frac{\mathrm{\sigma }}{2{\mathrm{\epsilon }}_0}=\frac{\mathrm{\sigma }}{{\mathrm{\epsilon }}_0} \\ \mathrm{but} \mathrm{outside} \mathrm{they} \mathrm{are} \mathrm{in} \mathrm{the} \mathrm{oppostie} \mathrm{direction} \mathrm{hence} \mathrm{net} \mathrm{E}=0 \end{gathered}$$