The field from a potential in code

You will write three functions about potential and field. They use $E = -dV/dx$ and $V = kq/r$.

The idea. A potential can be given as a Python function V(x). The field is minus the slope, and the slope can be found from a tiny step on each side of $x$. For a point charge, an equipotential surface is a sphere.

Your tasks.

1. In field_from_potential, return $E = -dV/dx$ at the position x. Use the potential at x + h and at x - h.
2. In sphere_radius, return the radius in m of the equipotential sphere with potential V round a point charge q in C.
3. In surface_gap, return the distance in m between the sphere at V_high and the sphere at V_low round the same positive charge.