Stereo Vacuum Tube Amplifiers

Current through a Capacitor

         A request has been made, via this website, for an explanation as to how an electric current passes through a capacitor - a passive, electronic component comprising two electrically conductive plates in close proximity, separated by an insulator.


        Whilst this website does not offer tutorials, it shall provide a simple answer to the above for those few, curious questioners. 

           As a changing electric current electrifies a capacitor plate, a proportional magnetic field is established & thence a displacement current (a time-varying electric field) which passes freely through the dielectric material to the opposite plate.  Displacement current is a variant form of electric/electron current & does not observe Ohm's Law; it streams effortlessly through free space & dielectric materials in the same way electric current flows along a conductor.  This curiosity is the vehicle by which fluctuating signals are transposed & transported through a capacitor - think audio signal conveyance by virtue of mutual inductance.

          Capacitive reactance, denoted by Xc, is the frequency dependant resistance of a capacitor calculated using the formula: 

                                                       Xc   =   1/f c (6.28)

          where is frequency in Hertz (Hz) & c is capacitance in Farads (F).

          By substituting values into the formula, it will be noted that Xc decreases with increasing frequency.  Higher frequencies stimulate & intensify field activity within the device itself owing to their amassed energy; this heightened activity serves to reduce Xc.  The entire process is basic physics - the science concerned with the properties & changes of matter & energy.

          Direct current (DC) does not pass through a capacitor.

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