Electric field at a point varies as $r^o$ for

Consider a cube of uniform charge density $\rho$. The ratio of electrostatic potential at the centre of the cube to that at one of the corners of the cube is

A parallel plate capacitor has circular plates of $10\, cm$ radius separated by an air-gap of $1\, mm$ . It is charged by connecting the plates to a $100\, volt$ battery. Then the change in energy stored in the capacitor when the plates are moved to a distance of $1\, cm$ and the plates are maintained in connection with the battery, is

Consider a solid insulating sphere of radius $R$ with charge density varying as $\rho = \rho _0r^2$ ($\rho _0$ is a constant and $r$ is measure from centre). Consider two points $A$ and $B$ at distance $x$ and $y$ respectively $(x < R, y > R)$ from the centre. If magnitudes of electric fields at points $A$ and $B$ are equal, then 

An electric point charge $10^{-3}\,\mu C$ is placed at the origin $(0, 0)$ of $X-Y$ co- ordinate system. Two points $A$ and $B$ are situated at $(\sqrt 2, \sqrt 2)$ and $(2, 0)$ respectively. The potential difference between the points $A$ and $B$ will be.....$volt$

Three plates of common surface area $A$ are connected as shown. The effective capacitance will be