Electric field lines inside a spherically charged shell containing charge Given a spherical shell composed of protons (a hypothetical construct), how would one draw the electric field lines inside the shell if a proton is placed at the center of the shell?
The question is not answered here: Charge inside a charged spherical shell
 A: 
Given a spherical shell composed of protons (a hypothetical construct), how would one draw the electric field lines inside the shell if a proton is placed at the center of the shell ?

Assuming that the protons are evenly distributed on the shell surface, the electric field will be as follows:

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*Within the shell, there will be field lines extending radially out from the center. The total flux around the center will be equivalent to one proton. The flux density will decrease according to the inverse square law.


*Outside the shell, there will be field lines extending radially outward. The total flux around the shell will be equivalent to the sum of all the protons, both in the center and in the shell. The flux density will appear as if all the protons were in the center, and will decrease according to the inverse square law.
The reason for the shape of the field is this. Inside the shell, the influence all the protons on the shell cancel out. Outside the shell, the influence of all the protons on the shell have the same effect as if they were concentrated at the center. This applies is true for spherical shells with even charge distribution, but is not true of shells in general, i.e. it is not true of shells with arbitrary shapes.
A: Interesting question. The "spherical shell" in the problem, however, needs to be clarified, which leads to the following two cases.
Say we have a proton charged $q$ at the centre, and $N$ protons on the shell. A key fact to note is that there is a fundamental difference between (1) a conducting spherical "shell" carrying charge $Nq$ and (2) a distribution of $N$ protons equally spaced on an imaginary sphere centred around the central charge.
Refer to the (roughly drawn) diagram below.


*

*In the first case, the conducting media allows a charge of $-q$ to be induced on the inner side, terminating the electric field lines originating from the central charge. At the same time, a charge of $Nq + q$ is induced on the outer side, which results in the radial electric field lines outside.


*In the second case, which I assume is what the OP asked about,
what @MathKeepsMeBusy said in the comments is right. The field lines all terminate at infinity. In this case, there are $N$ discrete point charges that form some sort of spherical enclosure; they have no volume and cannot be infinitely close to each other, since that would mean we need an infinitely large constraint force to hold them in place. This in term means there will be spacing between them for the field lines to "pass through" radially (in yellow). On the other hand, field lines originating from charges on the shell (in blue) will also terminate at infinity. Only a part of the field lines are drawn for clearer view.
As a sidenote, you would find that the field outside, as calculated by Gauss's law, is the same for both cases.
