Electric field in a spherical capacitor.

[Felpudio]

Homework Statement

The potential difference Δϕ between the plates of a spherical capacitor is kept constant. Show that then the electric field at the surface of the inner sphere will be a minimum if a=(1/2)b, find that minimum.
Where: a=radius of the inner sphere, b=radius of the outside sphere.

Homework Equations

The potential difference between the plates is Δϕ=(Q/4πϵ_0)(1/b-1/a)

 

[BvU]

Hi Fel, welcome to PF !

There is something special about the PF homework part you need to know: the guidelines require you present an attempt at solution !

So no point in erasing part 3 of the template: we can't help until you show an effort!

The Attempt at a Solution

For a start, you might bring in an equation for the electric field at the surface of the inner sphere, expressed in a and $\Delta \phi$.