Question

Two identical balls of mass $m=0.9g$ each are charged by the same charges, joined by a thread and suspended from the ceiling (Figure). Find the charge (in $\mu C$) that each ball should have so that the tension in both the threads are same? The distance between the centres of balls is $R=3m$.

Answer 1

$\begin{array}{c}{T}_2+\frac{K{q}^2}{9}=T_1+0.009\\ T_1=\frac{K{q}^2}{9}+0.009\\ T_1=T_2\\ \frac{K{q}^2}{9}=0.009\\ q^2=\frac{9\times 9\times {10}^{-3}}{9\times {10}^9}\\ q=3\times {10}^{-6}C\\ q=3\mu C\end{array}$