Capacitors

### Capacitance

a) What must be the radius of a conducting sphere, located in the vacuum, so that its capacity is 1 F;
b) Assuming the planet Earth as a perfect sphere of radius equal to 6400 km, what is its capacitance?
Assume the Coulomb constant as. $$k_{0}=9 \times 10^{9}\;\frac{\text{N.m}^{2}}{\text{C}^{2}}$$