$A$ hollow metallic sphere of radius $R$ is given a charge $Q$. Then the potential at the centre is

Three charges each of value $+q$ are placed at the corners of an isosceles triangle $ABC$ with sides $AB = AC = 2a$. The midpoints of $AB$ and $AC$ are $D$ and $E$ respectively. The work done in taking a charge $Q$ from $D$ to $E$ is (where $\varepsilon_0$ is the permittivity of free space):

$A$ regular hexagon of side $6 \ cm$ has a charge of $2 \ \mu C$ at each of its vertices. What is the potential at the centre of the hexagon? $\left[\frac{1}{4 \pi \epsilon_0}=9 \times 10^9 \text{ SI units}\right]$

Three charges,each $+q$,are placed at the corners of an isosceles triangle $ABC$ with sides $BC = AC = 2a$. $D$ and $E$ are the midpoints of $BC$ and $AC$,respectively. The work done in taking a charge $Q$ from $D$ to $E$ is

The mass of a particle is $400$ times that of an electron and its charge is double that of an electron. The particle is accelerated by a potential difference of $5 \; V$. If the particle was initially at rest,what will be its final kinetic energy in $eV$?

Eight small drops,each of radius $r$ and having same charge $q$,are combined to form a big drop. The ratio between the potentials of the bigger drop and the smaller drop is