
$=120\, \mu \mathrm{C}$
Now when $S_{2}$ closed, suppose common potential $=$ $\mathrm{V}$
charge on $\mathrm{C}_{1}=\mathrm{q}_{1}$
and charge on $\mathrm{C}_{2}=\mathrm{q}_{2}$
So, $ \mathrm{q}_{1}=\mathrm{C}_{1} \mathrm{V}$ and $\mathrm{q}_{2}=\mathrm{C}_{2} \mathrm{V}$
$\frac{\mathrm{q}_{1}}{\mathrm{q}_{2}}=\frac{\mathrm{C}_{1}}{\mathrm{C}_{2}} \Rightarrow \frac{\mathrm{q}_{1}}{\mathrm{q}_{2}}=\frac{6}{3}=2 \Rightarrow \mathrm{q}_{1}=2 \mathrm{q}_{2}$
Also $\mathrm{q}_{1}+\mathrm{q}_{2}=\mathrm{q} \Rightarrow 2 \mathrm{q}_{2}+\mathrm{q}_{2}=\mathrm{q}$
$\Rightarrow \mathrm{q}_{2}=\frac{\mathrm{q}}{3}=\frac{120 \times 10^{-6}}{3}$
$=40\, \mu \mathrm{C}$

$V\left( {x,y,z} \right) = \left\{ {\begin{array}{*{20}{c}}
{0\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,for\,x\, < \, - d}\\
{ - {V_0}{{\left( {1 + \frac{x}{d}} \right)}^2}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,for\, - \,d\, \le x < 0}\\
{ - {V_0}\left( {1 + 2\frac{x}{d}} \right)\,\,\,\,\,\,\,\,\,\,\,for\,0\, \le x < d}\\
{ - 3{V_0}\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,for\,x\, > \,d}
\end{array}} \right.$
where $-V_0$ is the potential at the origin and $d$ is a distance. Graph of electric field as a function of position is given as



