What do the tubes of the air capacitor represent in an electrical capacitor?

The parallel conducting plates

The source of electrical current

The insulation between plates

The charged plate of a magnetic field

The tubes of the air capacitor represent the parallel conducting insulation between plates.

Explanation:

Air capacitors are capacitors which use air as their dielectric. The simplest air capacitors are made of two conductive plates separated by an air gap. Air capacitors can be made in a variable or fixed capacitance form.

Air capacitor is a mechanical model of electrical capacitor. The tubes represents insulation between the plates as it prevents the flow of air across the air-capacitor, in the same way that insulation prevents the flow of charge across the electrical capacitor.

The tubes represent the parallel conducting plates because they provide the main surfaces between the outside and inside.