A charge of $4\,\mu C$ is to be divided into two. The distance between the two divided charges is constant. The magnitude of the divided charges so that the force between them is maximum, will be.

Two point charges $ + 3\,\mu C$ and $ + 8\,\mu C$ repel each other with a force of $40\,N$. If a charge of $ – 5\,\mu C$ is added to each of them, then the force between them will become….$N$

Consider three charges $q_{1}, q_{2}, q_{3}$ each equal to $q$ at the vertices of an equilateral triangle of side $l .$ What is the force on a charge $Q$ (with the same sign as $q$ ) placed at the centroid of the triangle, as shown in Figure 

$A$ and $B$ are two identical blocks made of a conducting material. These are placed on a horizontal frictionless table and connected by a light conducting spring of force constant $‘K’$. Unstretched length of the spring is $L_0$. Charge $Q/2$ is given  to each block. Consequently, the spring stretches to an equilibrium length $L$. Value of $Q$ is