Four point charges $q_{A}=2\; \mu C, q_{B}=-5\; \mu C,$ $q_{C}=2\; \mu C,$ and $q_{D}=-5\;\mu C$ are located at the corners of a square $ABCD$ of side $10\; cm .$ What is the force on a charge of $1 \;\mu C$ placed at the centre of the square?

Two small conducting spheres of equal radius have charges $ + 10\,\mu C$ and $ – 20\,\mu C$ respectively and placed at a distance $R$ from each other experience force ${F_1}$. If they are brought in contact and separated to the same distance, they experience force ${F_2}$. The ratio of ${F_1}$ to ${F_2}$ is

Write some important points for vector form of Coulomb’s law.

The plates $S$ and $T$ of an uncharged parallel plate capacitor are connected across a battery. The battery is then disconnected and the charged plates are now connected in a system as shown in the figure. The system shown is in equilibrium. All the strings are insulating and massless. The magnitude of charge on one of the capacitor plates is: [Area of plates = $A$]