The minimum work needed to be done to bring a charge $q=6 \mu C$ from $\infty$ to a point $0.75 \ m$ from a charge $Q=30 \mu C$ is (in $J$)

Three charged concentric nonconducting shells are given as shown in the figure. Find the potential at point $A$.

Two identical metal balls of radius $r$ are at a distance $a$ $(a \gg r)$ from each other and are charged,one with potential $V_1$ and other with potential $V_2$. The charges $q_1$ and $q_2$ on these balls in $CGS$ $esu$ are

$A$ hollow charged metal sphere has radius $R$. If the potential difference between its surface and a point at a distance $5R$ from the centre is $V$,then the magnitude of the electric field intensity at a distance $5R$ from the centre of the sphere is:

$A$ potential at a point $A$ is $-3 \ V$ and that at another point $B$ is $5 \ V$. What is the work done in carrying a charge of $5 \ mC$ from $B$ to $A$?

Two point charges $-q$ and $+q$ are located at points $(0,0,-a)$ and $(0,0, a)$ respectively. The electric potential at a point $(0,0, z)$,where $z>a$ is