Why isn't there a current in between the two plates in a capacitor?

Question

anonymous · Answer

capacitors are purposely designed to not allow current flow between the plates... there is a physical separation between the plates, either filled with air, vacuum or a polarizable medium called a dielectric. If a current flows, the capacitor is defective and must be replaced in the circuit. What you want to do with a capacitor in the simplest case is to cause it to collect and store charge (or energy).

anonymous · Answer

How does the current pass through in order to complete the circuit if there is actual current in between the plates?

anonymous · Answer

*is not

anonymous · Answer

it doesn't... the charge is pumped from one plate to the other by the battery (the potential difference). If you are using "conventional current flow" the positive charges are caused to move from the "bottom" plate to the top plate by the electric field maintained in the wire by the battery

anonymous · Answer

Okay, thanks for clearing that up.

anonymous · Answer

Suplimentary to the above, you can make current pass through a capacitor if you increase the voltage across it to a high enough threshold..  this results in dielectric breakdown.  The capacitor is effectively damaged by this, and will no longer function as a capacitor though, so its not advisable.

Also, with  AC voltages, there will be some current within the dielectric material of the capacitor due to reorientation of the electric dipoles (polarisation) with the changing electric field.  This is a source of intrinsic dielectric loss.

In reality there is no such thing as a perfect insulator as at best they can be thought of as wide bandgap semiconductors, and material defects will be sources of charge carriers within the material.  So even if you charged a capacitor, and disconnected it from the circuit, it would still loose its charge due to current leakage through the material.

Finally, in capacitors in which the distance between the plates is of the order of 1 or 2 nanometres or less, current appears to flow across it due to quantum mechanical tunnelling.