Principle of Superposition

Two point charges $+q$ each, lying on a straight line are separated by a distance and another point charge $-2q$ is placed midway on the same straight line. Find the net force acting on the charge placed at midpoint.

Three charges, each of value q, are placed at the corners of an equilateral triangle. A fourth charge Q is placed at the centre of the triangle.

(ii) For what value of Q will the charges remain stationary? In  this situation, how much work is done in removing the charges to infinity ?

Three charges, each of value q, are placed at the corners of an equilateral triangle. A fourth charge Q is placed at the centre of the triangle. 

If $Q=-q$, will the charges at the corners move towards the centre or fly away from it towards the centre or fly away from it ?

Three point charges of $+2\mu C,-3\mu C$ and $-3\mu C$ are kept at the vertices A, B and C respectively of an equilateral triangle of side $20 \mathrm{cm}$ as shown in the Fig. $2.104$. What should be the sign and magnitude of the charge to be placed at the mid point (M) of side BC so that the charge at A remains in equilibrium?

Two particles A and B having charges $8\times {10}^{-6}$ coulomb and $-2\times {10}^{-6}$ coulomb respectively are held fixed with separation of $20 \mathrm{cm}$. Where should a third charged particle be placed so that it does not experience any electric force?

Three identical small spheres weighing $0.1\mathrm{gm}$ are suspended from a point with silk threads each having length $20 \mathrm{cm}$. What charges should be imparted to the spheres so that each thread makes an angle $30°$ to the vertical? Assume the charges to be equal.

Charges of $+2,+3$ and $-8\mathrm{\mu C}$ are placed at the vertices of an equilateral triangle of side $10 \mathrm{cm}$. Calculate the magnitude of the force acting on the $-8\mathrm{\mu C}$ charge due to the other two charges. 

Two particles A and B having charges $8\times {10}^{-6}$ coulomb and $-2\times {10}^6$ coulomb respectively are held fixed with a separation of $20 \mathrm{cm}$. Where should a third charged particle be placed so that it does not experience any electric force?

Five point charges, each of value $+q$ coulomb, are placed on five vertices of a regular hexagon of side $L$ metre. The magnitude of the force on the point charge of value $-q$ coulomb placed at the center of the hexagon is $\frac{q^2}{k{\mathrm{\pi \epsilon }}_0{\mathrm{L}}^2}$ newton. Value of k is _____

A charge $q_1$ exerts a force on a second charge $q_2$. A third charge $q_3$ is brought near. Then force exerted by $q_1$ on $q_2$ will - 

Three charges $4q$, $Q$ and $q$ are placed in a straight line of $0, \frac{l}{2}$ and $l$ respectively. What should be $Q$ at length $l$ at points in order to make the net force on $q$ to be zero ?