Three point charges $1C, 2C, 3C$ are placed at the corners of an equilateral triangle of side $1m$. The work required to move these charges to the corners of a smaller equilateral triangle of side $0.5m$ is

Initial potential energy of the system, $\mathrm{U}=\frac{1}{4\pi {\epsilon }_{\mathrm{o}}}[\frac{{\mathrm{q}}_1{\mathrm{q}}_2}{\mathrm{r}}+\frac{{\mathrm{q}}_2{\mathrm{q}}_3}{\mathrm{r}}+\frac{{\mathrm{q}}_1{\mathrm{q}}_3}{\mathrm{r}}]$

$U_1=9\times {10}^9\left[1\times 2+2\times 3+1\times 3\right]$

$=9\times {10}^9\times 11=9.9\times {10}^{10}\text{\hspace{0.17em}J}$

Final potential energy of the system,

$U_2=\frac{9\times {10}^9}{0.5}\left[1\times 2+2\times 3+1\times 3\right]$

$=9\times {10}^9\times 22=19.8\times {10}^{10}\text{\hspace{0.17em}J}$

Work done in changing the configuration,

$\mathrm{W}={\mathrm{U}}_{\mathrm{F}}-{\mathrm{U}}_{\mathrm{I}}$

$=19.8\times {10}^9-9.9\times {10}^{10}=9.9\times {10}^{10}\text{\hspace{0.17em}J}$