# How far should the two circular conducting plates each of radius 20/√π cm be kept in vacuum to constitute a parallel plate capacitor of capacitance 40 of?

A = $\pi r^{2}$ = 400 cm*cm = 0.04 m*m
Capacitance C = A$\varepsilon$0/d
So d = 0.04$\varepsilon$0/40 =  8.85*10-15 m