Quote Originally Posted by GM View Post
...so by leakage current, are you referring to the cap's conductance due to the electrical circuit's capacitive reactance WRT frequency or......? ...
Consider a caps' construction. Two conductive 'plates' are separated by a very thin, non-conductive dielectric material. No way for current to flow unless the breakdown voltage of the dielectric is exceeded, or the dielectric is damaged in some other way, such as deterioration of the dielectric oxide in electrolytic caps. Leakage current is undesirable, it's the result of the dielectric material being a less-than-perfect insulator and passing a negligable current flow. Leakage is also the reason a charged, out-of-circuit cap will eventually discharge itself.

The mechanical analogy I was taught was that of a thin rubber diaphragm stretched across a water pipe, where the water pressure represents voltage. As the pressure (voltage) on one side of the diaphragm increases, the diaphragm stretches towards the side of lower pressure, forcing water movement in that direction. As the pressure decreases, the stored energy is discharged, and the cycle reverses in direction, following the alternating pressure source. Energy is transferred, but no current actually passes thru the diaphragm, save for a tiny bit of leakage through a pinhole (imperfect insulator). Exceed the pressure the diaphragm can withstand, (breakdown voltage) and it bursts, allowing flow (a short).

Another telltale sign is that caps have no current or dissipation rating as do all conductors or resistive devices that actually carry current. Nor do they produce the heat indicative of power dissipation.

I found this animated gif that shows a similar analogy in a smoothing application, as used in a power supply;

capwater