I think I got it!!!!
Suppose u is the energy density, then
u = ½ E0 E2.
And also according to gauss theorem, if r is the distance from the centre, then electric field at a distance r is
E= 1/4piE0 (q/r2)
Energy store in dr thickness is
dU=1/2 E0 E2 (4pi r2 dr)
we will put the value of E.
dU = ½ E0 [1/4piE0 (q/r2)] ((4pi r2 dr)
dU= (q2/ 16piE0 ). (2pi dr)
dU= q2 dr/r2
if u integrate this
U= q2/ 8piE0 [ ]
[ ] dr/r2 {note from R to infinity) { R is radius}
U= q2 / 8pi E0 R
Phew!!! Hope dis is the ans!!!
