Example $8\mathrm{.}3$

A capacitor for displacement measurement consists of two disks $25mm$ in diameter. What will

the capacitance be if the distance between them is

$($a$)0\mathrm{.}025mm,$

$($b$)0\mathrm{.}05mm,$ and

$($c$)0\mathrm{.}10mm?$