Charges of $2 \mu C$ and $-3 \mu C$ are placed at two points $A$ and $B$ separated by a distance of $1 \ m$. The distance of the point from $A$ where the net potential is zero is: (in $m$)

Two concentric hollow conducting spheres of radius $r$ and $R$ $(r < R)$ are shown. The charge on the outer shell is $Q$. What charge $q$ should be given to the inner sphere so that the potential at any point $P$ at a distance $x$ $(x > R)$ from the center is zero?

Which of the following statements is correct?

$A$ ball of mass $1\, g$ and charge $10^{-8}\, C$ moves from a point $A$,where the potential is $600\, V$,to a point $B$,where the potential is $0\, V$. The velocity of the ball at point $B$ is $20\, cm/s$. The velocity of the ball at point $A$ will be:

Two charges $q_1$ and $q_2$ are fixed at points $A$ and $B$ respectively, separated by a distance of $30 \text{ cm}$. $A$ third charge $q_3$ is moved along a circular path of radius $40 \text{ cm}$ from point $C$ to point $D$. If the difference in potential energy due to the movement of $q_3$ from $C$ to $D$ is $q_3 K / (4 \pi \epsilon_0)$, find the value of $K$. (Given: $AC = 40 \text{ cm}$, $AB = 30 \text{ cm}$, $AD = 40 \text{ cm}$)

An infinite number of charges,each equal to $0.2\,\mu C$,are arranged in a line at distances $1\,m, 2\,m, 4\,m, 8\,m, \dots$ from a fixed point. The potential at the fixed point is $......\,kV$.