A thin spherical shell of radius $R$ carries uniform surface charge density $\sigma .$ It is cut into two parts by a plane at a distance $\frac{R}{\sqrt{2}}$ from centre as shown. To hold two parts together force $F$ from both side has to be applied. The minimum force $F$ is $\frac{3\pi {\sigma }^2{R}^2}{n{\epsilon }_0}.$ Value of $n,$ is

An infinitely large layer of charge of uniform thickness $t$ is placed in existing uniform electric field. Presence of this charged layer so alters the electric field that it remains uniform on both the sides and assumes values $E_1$ and $E_2$ as shown in figure. If, $\left|{\overrightarrow{E}}_2\right|=20 \mathrm{N} {\mathrm{C}}^{-1}$ Then component of external field in $x$-direction (in $\mathrm{N} {\mathrm{C}}^{-1}$) is