Two conducting spheres of radii $r_1$ and $r_2$ are charged to the same surface charge density. The ratio of electric fields near their surfaces is

Two electric charges $+2 \mu \mathrm{C}$ and $-4 \mu \mathrm{C}$ are separated by a distance 3 m in air. At a point $P$ located on the line joining the two charges and in between them, the electric potential is zero. Then the electric field at a point $P$ (in $\mathrm{NC}^{-1}$ ) is

The flux of the electric field $\mathbf{E}=24 \hat{\mathbf{i}}+30 \hat{\mathbf{j}}+28 \hat{\mathbf{k}} \mathrm{NC}^{-1}$ through an area of $20 \mathrm{~m}^2$ on the $Y Z$-plane is

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