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.)

The force on a charge situated on the axis of a dipole is $F$. If the charge is shifted to double the distance, the new force will be

The plates of a parallel plate capacitor are charged up to $100\, volt$. A $2\, mm$ thick plate is inserted between the plates, then to maintain the same potential difference, the distance between the capacitor plates is increased by $1.6\, mm$. The dielectric constant of the plate is

A charge $q$ is placed at $O$ in the cavity in a spherical uncharge $d$ conductor. Point $S$ is outside the conductor. If the charge is displaced from $O$ towards $S$ still remaining with in the cavity,

Four metallic plates, each with a surface area of one side $A$, are placed at a distance $d$ from each other. The plates are connected as shown in the figure. The capacitance of  the system between $a$ and $b$ is

A negative charged particle is released from rest in a uniform electric field. The electric potential energy of charge