I have some questions about the Gauss's law for electric field. Wikipedia definition says
The electric flux through any closed surface is proportional to the enclosed electric charge
Now how did Mr Gauss arrive at this conclusion regarding any closed surface ?
That is a very general statement. And during his time, were there instruments which could have lead to the formulation of such general principles ?
And can you please explain this without "electric field lines" since they are not
physically real lines ?