Three charges $+5 q, Q$ and $-2 q$ are kept along a straight line in the same order such that, $+5 q$ and $-2 q$ charges are at a distance of $\frac{2 r}{3}$ and $\frac{r}{3}$ from the charge $Q$ respectively. If the net force on the charge $-2 q$ is zero, then $Q$ is

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Aicharya · Accepted Answer

The given situation is shown below.

Since, net force on charge $(-2 q)$ is zero, Therefore, charge $Q$ must be positive so that there are two opposing forces on charge $-2 q$. Now, $\quad F_{\text {net }}=0$ i.e. $\quad F(5 q,-2 q)=F(Q,-2 q)$ $\Rightarrow \quad \frac{K .5 q \times(-2 q)}{r^2}=\frac{-K . Q \times 2 q}{\left(\frac{r}{3}\right)^2}$ $\Rightarrow \quad 10 q=2 \times 9 \times Q \Rightarrow Q=\frac{5}{9} q$

Three charges $+5 q, Q$ and $-2 q$ are kept along a straight line in the same order such that, $+5 q$ and…

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