# Source: /cirosantilli/capacitor

= Capacitor
{wiki}

The fundamental intuition about capacitors is that they never let <electrons> through.

They can only absorb <electrons> up to a certain point, but then the pushback becomes too strong, and current stops.

Therefore, they cannot conduct <direct current> long term.

For <alternating current> however, things are different, because in alternating current, <electrons> are just jiggling back and forward a little bit around a center point. So you can send alternating current power across a capacitor.

The key equation that relates <Voltage> to <electric current> in the <capacitor> is:
$$I(t) = C \dv{V(t)}{t}$$
So if a voltage <Heavyside step function> is applied what happens is:
* the capacitor fills up instantly with an infinite current
* the current then stops instantly
More realistically, one may consider the behaviour or the <series RC circuit> to see what happens without infinities when a capacitor is involved as in the <step response of the series RC circuit>.