What will be the magnitude of electric field at point $O$ as shown in figure ? Each side of the figure is $I$ and perpendicular to each other.

Infinite charges of magnitude $q$ each are lying at $x =1,\, 2,\, 4,\, 8…$ meter on $X$-axis. The value of intensity of electric field at point $x = 0$ due to these charges will be

Charges $q$, $2q$, $3q$ and $4q$ are placed at the corners $A$,$ B$,$ C$ and $D$ of a square as shown in the following figure. The direction of electric field at the centre of the square is along

Three identical point charges, as shown are placed at the vertices of an isosceles right angled triangle. Which of the numbered vectors coincides in direction with the electric field at the mid-point $M$ of the hypotenuse

Write equation of electric field by system of $\mathrm{'n'}$ charges.