In space the electric potential varies as $V=20|\mathbf{r}|$ volt. where $\mathbf{r}=x \hat{\mathbf{i}}+y \hat{\mathbf{j}}+z \hat{\mathbf{k}}$ is the position vector. Then, electric field in $\left(\mathrm{NC}^{-1}\right)$ at the point $(4 \mathrm{~m}, 3 \mathrm{~m},-5 \mathrm{~m})$ is

The sum of two point positive charges separated by a distance of 1.5 m in air is $25 \mu \mathrm{C}$. If the electrostatic force between the two charges is 0.6 N , then the difference between the two charges is

A solid of mass 1 kg has $6 \times 10^{24}$ atoms. If one electron is removed from every one atom of $0.005 \%$ of the atoms, then the charge gained by the solid is

If the energy stored in a spherical conductor having a charge of $12 \mu \mathrm{C}$ is 6 J , then the radius of the spherical conductor is