Three charges $-q, Q$ and $-q$ are placed respectively at equal distances on a straight line. If the potential energy of the system of three charges is zero, then what is the ratio of $Q: q$ ?
Medium
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(d)
$U=\frac{-k q Q}{x}-\frac{k q Q}{x}+\frac{k q^2}{2 x}=0$
$\frac{k q^2}{2 x}=\frac{2 k q Q}{x}$
$q=4 Q,$
$\frac{Q}{q}=\frac{1}{4}$
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