In the figure shown, the potential difference between points $A$ and $B$ is......$V$

A parallel plate capacitor is charged to a potential difference of $100\ V$ and disconnected from the source of emf. A slab of dielectric is then inserted between the plates. Which of the following three quantities change?

$(i)$ The potential difference
$(ii)$ The capacitance
$(iii)$ The charge on the plates

Two spheres of radius $a$ and $b$ respectively are charged and joined by a wire. The ratio of electric field of the spheres is

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 

In a hollow spherical shell, potential $(V)$ changes with respect to distance $(s)$ from centre as

Two equal point charges are fixed at $x = -a$ and $x = + \,a$ on the $x$-axis. Another  point charge $Q$ is placed at the origin. The change in the electrical potential energy of $Q$ ehen it is displaced by a small distance $x$ along the $x$ -axis is apporximately proportional to