Calculating the Increase in Energy for a Capacitor with Concentric Spheres

[renegade05]

Homework Statement

A capacitor consisting of two concentric spheres is arranged so that
the outer sphere can be separated and removed without disturbing the
charges on either. The radius of the inner sphere is a and that of the outer
sphere is b, and the charges are Q and -Q, respectively

a) If the outer sphere is removed and restored to its original form, find the
increase in energy when the two spheres are separated by a large distance.

b) Where does this extra energy come from?

Homework Equations

no idea

The Attempt at a Solution

no idea

The professor is teaching at a way higher level than necessary and I have no clue on what to do. Do I use gauss' law? maybe? I have no idea. please help

 

[Simon Bridge]

How do you normally work out the energy stored in a configuration of charges?
You should have some notes on this.

 

[zoki85]

@renegade05, think of difference of electrostatic energies between two cases. Capacity of spherical capacitor is:

Capacity of isolated sphere is?
And formula for electrostatic energy you will use is?