Question

The plates of a parallel – plate capacitor uses a disk with a radius of 10mm. The separation distance between the plates is 100 nm and between the plates is a sheet of mica. What is the capacitance of the capacitor? 

Answer 1

$$C=\frac{\epsilon\epsilon_0A}{d}$$

$$C=\frac{5*8.85*10^{-12}*3.14*0.005^2}{100*10^{-9}}\\ =3.5*10^{-8}\:\rm F=35\: nF$$