A capacitor is to be designed to have a capacitance of 4.7 pF and to operate with a p.d. of 120 V across its terminals. The dielectric is to be teflon ( εr = 2.1) which, after allowing for a safety factor has a dielectric strength of 25 kV/m. Calculate
(a) the thickness of teflon required and
(b) the area of a plate.