Three equal charges are placed at the corners of an equilateral triangle. Which of the graphs below correctly depicts the equally-spaced equipotential surfaces in the plane of the triangle? (All graphs have the same scale.)

Electric flux through surface $s_1$

Two equal charges are separated by a distance $d$. A third charge placed on a perpendicular bisector at $x$ distance will experience maximum coulomb force when

Five balls numbered $1$ to $5$ are suspended using separate threads. Pairs $(1,2), (2,4)$ and $(4,1)$ show electrostatic attraction while pairs $(2,3)$ and $(4,5)$ show repulsion. Therefore ball $1$ must be

A given charge situated at a distance $r$ from an electric dipole on it axis experiences a force $F$. If the distance of the charge from the dipole is doubled, the force acting on the charge will be

A thin spherical conducting shell of radius $R$ has a charge $q.$ Another charge $Q$ is placed at the centre of the shell. The electrostatic potential at a point $p$ a distance $R/2$ from the centre of the shell is