A body has $-80$ micro coulomb of charge. The number of additional electrons in it will be

A charge $Q_1$ exerts some force on a second charge $Q_2.$ If a third charge $Q_3$ is brought near, the force of $Q_1$ exerted on $Q_2$:

Two point charges of same magnitude and opposite sign are fixed at points $A$ and $B.$ A third small point charge is to be balanced at point $P$ by the electrostatic force due to these two charges. The point $P:$

Two small spherical balls each carrying a charge $Q=10 \mu \mathrm{C}$ ($10$ micro-coulomb) are suspended by two insulating threads of equal lengths $1 \mathrm{m}$ each, from a point fixed in the ceiling. It is found that is equilibrium threads are separated by an angle $60°$ between them, as shown in the figure. What is the tension in the threads (Given $\frac{1}{\left(4\pi {\epsilon }_0\right)}=9\times {10}^9 \mathrm{N} \mathrm{m} {\mathrm{C}}^{-2}$)-