Three charges $Q, +q$ and $+q$ are placed at the vertices of an equilateral triangle of side l, as shown in the figure. If the net electrostatic energy of the system is zero, the Q is equal to :
Answer & explanation
Correct answer: option 3
The correct answer is option (3) : $-\frac{q}{2}$
$U=\frac{kq^2}{l}+\frac{KqQ}{l}+\frac{kqQ}{l}$
Given, $U=0$
$=\frac{kq^2}{l}+\frac{2KqQ}{l}=0$
$Q=\frac{-q}{2}$