Find potential at point $P$ in the following cases:

Find the value of $k$ if potential at $O$ is zero.

Four charges $2 \mathrm{C}, -3 \mathrm{C}, -4 \mathrm{C} \& 5 \mathrm{C}$ respectively are placed at all the corners of a square. Which of the following statements is true for the point of intersection of the diagonals ?

Two charges $q$ and $-4 q$ are kept at points $A$ and $B$. Let $V$ be the potential at any point on the line joining $A$ and $B.$ The correct variation of $V$ along the $AB$ is

A rod is bent into a semi-circular arc of radius $R.$ The rod has a uniform linear charge distribution $\lambda .$ The potential at the centre of the arc, point $P$ is