Q. Two charges $Q_{1}$ and $Q_{2}$ are separated by $6\, cm .$ An electron at $2\, cm$ from $Q_{1}$ in between them experiences no force. If $Q_{1}=10 \,\mu C$, then $Q_{2}$ is equal to
Solution:
The electron is placed at the point $X$. It is at a distance of $2 \,cm$ from $Q_{1}$
$X=\frac{d}{\sqrt{\frac{Q_{2}}{Q_{1}}}+1}$
$ \Rightarrow 2=\frac{d}{\sqrt{\frac{Q_{2}}{10}}+1} $
$\Rightarrow Q_{2}-40\, \mu C$
