The electric potential at the surface of an atomic nucleus $(Z=50)$ of radius $9 \times 10^{-15} \ m$ is . . . . . . .

Which of the following graphs correctly represents the variation of electric potential $(V)$ of a charged spherical conductor of radius $(R)$ with radial distance $(r)$ from the centre?

Concentric metallic hollow spheres of radii $R$ and $4R$ hold charges $Q_1$ and $Q_2$ respectively. Given that surface charge densities of the concentric spheres are equal,the potential difference $V(R) - V(4R)$ is

Charges $+q$ and $-q$ are placed at points $A$ and $B$ respectively,which are a distance $2L$ apart. $C$ is the midpoint between $A$ and $B$. The work done in moving a charge $+Q$ along the semicircle $CRD$ is

Charges of $1 \mu C$ are placed at each of the four corners of a square of side $2 \sqrt{2} \text{ m}$. The potential at the point of intersection of the diagonals is . . . . . . .

Two concentric hollow spherical shells have radii $r$ and $R$ $(R \gg r)$. $A$ charge $Q$ is distributed on them such that the surface charge densities are equal. The electric potential at the centre is