# Three identical charges $\;(q)\;$ are placed at corners of an equilateral triangle of side l . Find the work require to double the dimensions of traingle

$(a)\;\large\frac{-3 \;k\; q}{l}\qquad(b)\;\large\frac{3 \;k \;q^2}{l}\qquad(c)\;\large\frac{3 \; q^2}{2 l}\qquad(d)\;\large\frac{-3 \;q^2}{2 l}$

Answer : (d) $\;\large\frac{-3 \; q^2}{2l}$
Explanation : $W_{done}=P\;.E_{final}-P\;.E_{initial}$
$=\large\frac{3\;k\;q^2}{2l}-\large\frac{3\;k\;q^2}{l}$
$=-\large\frac{3\;k\;q^2}{2l}\;.$