A parallel plate capacitor with plate area $$A$$ and separation between the plates $$d$$ is charged by a constant current $$i$$. Consider a plane surface of area $$A / 2$$ parallel to the plates and drawn simultaneously between the plates. The displacement current through this area is

A parallel plate capacitor of capacitance $$5 \mu \mathrm{F}$$ is charged to $$120 \mathrm{~V}$$ and then connected to another uncharged capacitor. If the potential falls to $$40 \mathrm{~V}$$, and capacitance of the second capacitor is

Two identical capacitors are first connected in series and then in parallel. The ratio of equivalent capacitance is