Point charges $+q$ and $-q$ are located at the vertices of a square with diagonals $2l$ as shown in the figure. The magnitude of the electric field strength at a point, located symmetrically with respect to the vertices of the square at a distance $x$ from its center is

A charge Q is uniformly distributed over a long rod AB of length L as shown in the figure. The electric potential at the point O lying at a distance L from the end A is :

An electron is placed on $X$-axis where the electric potential depends on $x$ as shown in figures (the potential does not depend on $y$ and $z$ ). What is the electric force on the electron?

The figure gives the electric potential $V$ as a function of distance through four regions on $x$-axis. Which of the following is true for the magnitude of the electric field $E$ in these regions?