The electric field and electric potential at a point due to a point charge are $500 \mathrm{NC}^{-1}$ and 30 V respectively, then the magnitude of the charge is

A clock dial has point charges $-q,-2 q,-3 q, \ldots \ldots \ldots,-12 q$ at the positions of the corresponding numbers on the dial respectively. The time at which the hour's hand points the direction of the net electric field at the centre of the dial is (Assume clock hands do not influence the net electric field)

The electric potential at a place is varying as $V=\frac{1}{2}\left(y^2-4 x\right) \mathrm{V}$. Then, the electric field at $x=1 \mathrm{~m}$ and $y=1 \mathrm{~m}$ is