This can be seen in the motion of the electric field lines as they move from the edge to the center of the capacitor. As the potential difference between the plates increases, the sphere feels an increasing attraction towards the top plate, indicated by the increasing tension in the field as more field lines "attach" to it.
To find the capacitance C, we first need to know the electric field between the plates. A real capacitor is finite in size. Thus, the electric field lines at the edge of the plates are not straight lines, and the field is not contained entirely between the plates.
A real capacitor is finite in size. Thus, the electric field lines at the edge of the plates are not straight lines, and the field is not contained entirely between the plates. This is known as edge effects, and the non-uniform fields near the edge are called the fringing fields.
As far as the field inside the capacitor is concerned, there tends to be no normal component of E. In the opposite extreme, where the region to the right has a high permittivity compared to that between the capacitor plates, the electric field inside the capacitor tends to approach the interface normally.
This electric field exists not just directly between the conductive objects, but extends some distance away, a phenomenon known as a fringing field. To accurately predict the capacitance of a capacitor, the domain used to model the fringing field must be sufficiently large, and the appropriate boundary conditions must be used.
When we find the electric field between the plates of a parallel plate capacitor we assume that the electric field from both plates is E = σ 2ϵ0n.^ E = σ 2 ϵ 0 n. ^ The factor of two in the denominator comes from the fact that there is a surface charge density on both sides of the (very thin) plates.