$A$ neutral spherical copper particle has a radius of $10 \,nm$ $(1 \,nm = 10^{-9} \,m)$. It gets charged by applying the voltage,slowly adding one electron at a time. Then,the graph of the total charge on the particle versus the applied voltage would look like:

Electric potential at a point $P$ due to a point charge of $5 \times 10^{-9} \; C$ is $50 \; V$. The distance of $P$ from the point charge is ......... $cm$. (Assume,$\frac{1}{4 \pi \varepsilon_0} = 9 \times 10^9 \; N m^2 C^{-2}$)

$A$ regular hexagon of side $5 \, cm$ has a charge $10 \, \mu C$ at each of its vertices. The potential at the centre of the hexagon is

Three charged particles having charges $q, -2q$,and $q$ are placed in a line at points $(-a, 0), (0, 0)$,and $(a, 0)$ respectively. The expression for electric potential at $P(r, 0)$ for $r \gg a$ is ...............

Two identical thin rings each of radius $R$ meters are coaxially placed at a distance $R$ meters apart. If $Q_1$ coulomb and $Q_2$ coulomb are respectively the charges uniformly spread on the two rings,the work done in moving a charge $q$ from the centre of one ring to that of other is

Four charges,each of value $Q = \frac{10}{3} \times 10^{-9} \ C$,are placed at the four corners of a square of side $a = 8 \ cm$. What is the electric potential at the center of the square?