A parallel plate capacitor is to be designed with a voltage rating of 1 \mathrm{kV}, using a material of dielectric constant 3 and dielectric strength of about 10^{7} \mathrm{Vm}^{-1}. (Dielectric strength is the maximum electric field a material can tolerate without breakdown, i.e., without starting to conduct electricity through partial ionisation.) For safety, we should like the field never to exceed, say 10 \% of the dielectric strength. What minimum area of the plates is required to have a capacitance of 50 \mathrm{pF} ?
A parallel plate capacitor is to be designed with a voltage rating of 1 \mathrm{kV}, using a material of dielectric constant 3 and dielectric strength of about 10^{7} \mathrm{Vm}^{-1}. (Dielectric strength is the maximum electric field a material can tolerate without breakdown, i.e., without starting to conduct electricity through partial ionisation.) For safety, we should like the field never to exceed, say 10 \% of the dielectric strength. What minimum area of the plates is required to have a capacitance of 50 \mathrm{pF} ?

Solution:

Voltage rating of the parallel plate capacitor, V=1 \mathrm{kV}=1000 \mathrm{~V}.

Dielectric constant, \varepsilon=3

Dielectric strength =10^{7} \mathrm{~V} / \mathrm{m}

For reasons of safety, the field should never exceed, say, ten percent of the dielectric strength, or 10 percent.of dielectric strength =(10 / 100) \times 10^{7}=10^{6} \mathrm{~V} / \mathrm{m}

Capacitance of capacitor, C=50 \mathrm{pF}=50 \times 10^{-12} \mathrm{~F}

Distance between the plates, d=V / E=10^{3} / 10^{6}=10^{-3} \mathrm{~m} Area of the plate, \mathrm{A}=A=\frac{d}{\epsilon_{0} \epsilon_{r} C}

=19 \mathrm{~cm}^{2}

Therefore, the minimum area of the plates evaluated is, A=19 \mathrm{~cm}^{2}