$A$ charge '$Q$' $C$ is placed at the centre of a cube. The electric flux through two opposite faces of the cube is $(\epsilon_0 = \text{permittivity of free space})$

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 $8.0 \times 10^{3} \; N m^{2} / C$.
$(a)$ What is the net charge inside the box?
$(b)$ 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?

If an electric charge $q$ is placed at the centre of a cube,then the flux associated with each surface of the cube is . . . . . . .

$A$ hollow cylinder has a charge $q$ coulomb within it. If $\phi$ is the electric flux in units of volt-meter associated with the curved surface $B$,the flux linked with the plane surface $A$ in units of volt-meter will be:

If the electric field is given by $\vec{E} = (5 \hat{i} + 4 \hat{j} + 9 \hat{k})$. The electric flux through a surface of area $20$ units lying in the $Y-Z$ plane will be (in units):

Why do electric field lines not form closed loops?