Four charges $+Q, -Q, +Q, -Q$ are placed at the corners of a square taken in order. At the centre of the square:

Four electric charges $+Q, -Q, +Q$,and $-Q$ are placed at the four corners of a square. What are the electric field $(E)$ and electric potential $(V)$ at the center of the square?

Two point charges $4\,\mu C$ and $-1\,\mu C$ are kept at a distance of $3\ m$ from each other. What is the electric potential at the point where the electric field is zero?

Two point charges $+q$ and $-q$ are held fixed at $(-d, 0)$ and $(d, 0)$ respectively of a $(X, Y)$ coordinate system. Then:

$A$ positively charged thin metal ring of radius $R$ is fixed in the $xy$-plane with its centre at the origin $O$. $A$ negatively charged particle $P$ is released from rest at the point $(0, 0, z_0)$,where $z_0 > 0$. Then the motion of $P$ is:

One moving electron when comes closer to another stationary electron,then its kinetic energy and potential energy respectively . . . . . . and . . . . . . .