Field and Wave Electromagnetics 2nd Edition by David Cheng

Exercise 39

Refer to Problem.
a) Calculate the time it takes for the charge density in the sphere to diminish to 1% of its initial value.
b) Calculate the change in the electrostatic energy stored in the sphere as the charge density diminishes from the initial value to 1% of its value. What happens to this energy
c) Determine the electrostatic energy stored in the space outside the sphere. Does this energy change with time
Problem:
Lightning strikes a lossy dielectric sphere- = 1.2 0 , = 10 (S/m)-of radius 0.1 (m) at time t = 0, depositing uniformly in the sphere a total charge 1 (mC). Determine, for all t,
a) the electric field intensity both inside and outside the sphere,
b) the current density in the sphere.