Question

graph of potential vs distance of a point charge​

Answer 1

area under a graph of electric field strength against distance, between two points, is the potential difference between those two points. ... If we double the distance between us and a point, the potential difference between us and that point will also double in a uniform electric field.

Answer 2

The potential at distance z is given by the following equation,

V(z)=σ2ε0[R2+z2−−−−−−√−|z|]

In the limiting case |z|≫R,

R2+z2−−−−−−√=|z|(1+R2z2)1/2

then the potential simplifies to

V≃σ2ε0R22|z|=14πε0σ(πR2)|z|=14πε0Q|z|

which is nothing but the potential for point charge.

Then the variation will be

You can see that the variation over large distances converges to that of a point charge.