= CR is called capacitive time constant, i.e. the time in which charge of the capacitor is 0.632 times of its maximum value during charging.
The charging current is I =
=
 = I0e– t/RC where I0 =
 =
.
At t = 0, I = I0 i.e. initially it acts as short circuit or as a simple conducting wire.
At t =
, I = 0 it acts as an open circuit.