Careful measurement of the electric field at the surface of a black box indicates that the net outward flux through the surface of the box is $8.0 \times {10}^3 {\mathrm{Nm}}^2\mathrm{C}$
If the net outward flux through the surface of the box were zero, could you conclude that there were no charges inside the box? Why or Why not?

Two large, thin metal plates are parallel and close to each other. On their inner faces, the plates have surface charge densities of opposite signs and of magnitude $17\times {10}^{-12} \mathrm{C}/{\mathrm{m}}^2$. What is $E$: a) in the outer region of the first plate b) in the outer region of the second plate and c) between the plates? Take, ${\in }_0=8.854\times {10}^{-12} {\mathrm{N}}^{-1}{\mathrm{C}}^2 {\mathrm{m}}^{-2}$.