Superposition Principle

A hemisphere is uniformly charged positively. The electric field at a point on a diameter away from the centre is directed

Three charges each of $+1 \mathrm{\mu }\mathrm{C}$ are placed at the corners of an equilateral triangle. If the force between any two charges be $F$, then the net force on either charge will be:

Two identical positive charges are fixed at $(0, b)$ and $(0,-b).$ A particle with negative charge starts from negative $x-$axis at a large distance from $O,$ moves along the $x-$axis, passes through $O$ and moves far away from $O.$ The particle's acceleration is $a\hat{i}.$ $a$ is plotted against its $x-$coordinate. Which of the following best represents the plot?

Three large identical conducting sheets, each having a surface area of $A$ is placed parallel to each other at finite distance contain charges $Q, -2Q$ and $3Q$. What is the magnitude of electric field at point$P$? 

Three charges, each of $q$ coulomb are placed as shown in the figure. Then the net force on the charge placed at the origin is -

Charges $+2\mathrm{q},\mathrm{ }+\mathrm{q}$ and $+\mathrm{q}$ are placed at the corners $\mathrm{A}$, $\mathrm{B}$ and $\mathrm{C}$ of an equilateral triangle $\mathrm{A}\mathrm{B}\mathrm{C}$. If $E$ is the electric field at the circumcentre $\mathrm{O}$ of the triangle, due to the charge $+\mathrm{q}$, then the magnitude and direction of the resultant electric field at $\mathrm{O}$ is:

Three charges each of $+1 \mathrm{\mu }\mathrm{C}$ are placed at the corners of an equilateral triangle. If the force between any two charges be $F$, then the net force on either charge will be,