A point charge $q$ is surrounded by eight identical charges at distance $r$ as shown in figure. How much work is done by the forces of electrostatic repulsion when the point charge at the centre is removed to infinity?
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(b)
$W=-q\left(V_f-V_i\right)=-q\left(V_{-}-V_i\right)=+q V_i$
$V_i=8 \cdot \frac{k q^2}{r}=\frac{8 q^2}{4 \pi \varepsilon_0 r}$
$W=\frac{+8 q^2}{4 \pi \varepsilon_0 r}$
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