Question

What is a Gaussian surface?A point charge of 2.0mueC at the centre of a cubic Gaussian surface 9.0cm on edge.What is the net electric flux through the surface?

Answer 1

a gaussian surface is any surface which enclose a charge. In this case, it is six sides. You have a neat theorem from Maxwell, that tells you the net flux is equal to the charge enclosed, divided by permitivity.
Gauss's Law. The total of the electric flux out of a closed surface is equal to the charge enclosed divided by the permittivity. The electric flux through an area is defined as the electric field multiplied by the area of the surface projected in a plane perpendicular to the field.
so net flux is the point charge/permitivity. The size of the cube does not matter.

Answer 2

The total electric flux linked with closed surface is equal one upon enot times the total inside surface
E propotinal one upon r square