Find out the surface charge density at the intersection of point $x =3\, m$ plane and $x$ -axis, in the region of uniform line charge of $8\, nC / m$ lying along the $z$ -axis in free space.

The electric field in a region is given by $\vec E = \frac{3}{5}{E_0}\hat i + \frac{4}{5}{E_0}\hat j$ and $E_0 = 2\times10^3\, N/C$. Then, the flux of this field through a rectangular surface of area $0.2\, m^2$ parallel to the $y-z$ plane is……$\frac{{N – {m^2}}}{C}$

Electric flux through surface $s_1$

The inward and outward electric flux for a closed surface in units of $N{\rm{ – }}{m^2}/C$ are respectively $8 \times {10^3}$ and $4 \times {10^3}.$ Then the total charge inside the surface is [where ${\varepsilon _0} = $ permittivity constant]

The black shapes in the figure below are closed surfaces. The electric field lines are in red. For which case, the net flux through the surfaces is non-zero?