Question

please who can explain to me capacitance of a spherical capacitor when a is far far greater than b

Answer 1

Start with the sphere of radius A surrounded by a spherical shell of radius B. Apply a voltage V such that 0 volts is on the shell B and V is on the sphere A. Calculate the capacitance. Then let radius B go to infinity.

Answer 2

for spherical capacitor capacitance \[C=4\pi \epsilon(ab)/(a-b)\]
or \[C=4\pi \epsilon(b)/{1-(b/a)}\]
a>>b then b/a is negligible...
then {1-(b/a)}~1
then \[C=4\pi \epsilon(b)\]