Question

Why does a capacitor never fully charge or discharge?

Answer 1

Charging of a capacitor is given by equation

$Q=Q_{0}(1-e^{\frac{-t}{RC}})$
and discharging of a capacitor is given by

$Q=Q_{0}(e^{\frac{-t}{RC}})$

where and $Q_{0}$ denote charge at any time't' and maximum charge on the capacitor.

From first equation, we can see that charge becomes maximum when t is equal to infinity. Likewise from second equation, we can see Q becomes zero when t is equal to infinity. Therefore, to completely charge or discharge a capacitor, infinite amount of time is required, hence a capacitor is never fully charged or discharged.