Calculating Charge and Current in a Region Between Concentric Conducting Spheres

[PhysicsUnderg]

Homework Statement

The region between concentric conducting spheres is filled with a material with conductivity σ and dielectric constant k. The inner sphere (radius a) is connected to the positive terminal of a battery with emf V_o, and the outer sphere (radius b) is connected to the negative terminal. At t=0 the batter is disconnected.
(a) Calculate Q(t), the charge on the inner conductor, and sketch a plot of this function. Show that the decay constant is kε_o/σ.
(b) Calculate I(t).

The Attempt at a Solution

How do I go about this question?

 

[tiny-tim]

Hi PhysicsUnderg!

Hint: what is the electric field between the spheres when the charge is q ?