What is called Gaussian surface ?

A point charge of $+\,12 \,\mu C$ is at a distance $6 \,cm$ vertically above the centre of a square of side $12\, cm$ as shown in figure. The magnitude of the electric flux through the square will be ....... $\times 10^{3} \,Nm ^{2} / C$

The electric field intensity at $P$ and $Q$, in the shown arrangement, are in the ratio

The figure shows the electric field lines of three charges with charge $+1, +1$, and $-1$. The Gaussian surface in the figure is a sphere containing two of the charges. The total electric flux through the spherical Gaussian surface is

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]

A positive charge $q$ is kept at the center of a thick shell of inner radius $R_1$ and outer radius $R_2$ which is made up of conducting material. If $\phi_1$ is flux through closed gaussian surface $S_1$ whose radius is just less than $R_1$ and $\phi_2$ is flux through closed gaussian surface $S_2$ whose radius is just greater than $R_1$ then:-