Three point charges are placed at the corners of an equilateral triangle. Assuming only electrostatic forces are acting
The system can never be in equilibrium
The system will be in equilibrium if the charges rotate about the centre of the triangle
The system will be in equilibrium if the charges have different magnitudes and different signs
The system will be in equilibrium if the charges have the same magnitudes but different signs
Four charges are arranged at the corners of a square $ABCD$, as shown in the adjoining figure. The force on the charge kept at the centre $O$ is
Two charges, each equal to $q$, are kept at $x = -a$ and $x = a$ on the $x-$axis. A particle of mass $m$ and charge $q_0=\frac{q}{2}$ is placed at the origin. If charge $q_0$ is given a small displacement $(y < < a)$ along the $y-$axis, the net force acting on the particle is proportional to
Three charge $q$, $Q$ and $4q$ are placed in a straight line of length $l$ at points distant $0,\,\frac {l}{2}$ and $l$ respectively from one end. In order to make the net froce on $q$ zero, the charge $Q$ must be equal to
Two spherical, nonconducting, and very thin shells of uniformly distributed positive charge $Q$ and radius d are located a distance $10d$ from each other. A positive point charge $q$ is placed inside one of the shells at a distance $d/2$ from the center, on the line connecting the centers of the two shells, as shown in the figure. What is the net force on the charge $q $ ?
Write value of Coulombian constant $k$ in $SI$ unit.