Hi,I just wanted to clarify something I am struggling to understand. I understand the concepts of AC and DC, but not capacitors and inductors.Why is it that Capacitors block DC current, but accept AC? Also, how do capacitors store energy from AC?Similarly, why do inductors short in DC, and how do they store energy?THANKS!
A capacitor consists of two metal 'plates' separated by a thin gap; the gap is filled with an insulator (the 'dielectric') such as air or plastic. The gap means that a (direct) current can't flow across it. Strictly speaking, alternating current doesn't 'flow through' anything - the electrons are just repeatedly going backwards and forwards a fraction of a mm without actually getting anywhere. When you apply an alternating voltage to a capacitor, in half of the cycle the capacitor charges up: one plate loses electrons and becomes positive; the other plate gains electrons and becomes negative. In the other half of the cycle, this is reversed (it's slightly more complex than this, but you get the picture). The plates are being alternately made positive/negative, then negative/positive by supplying and removing electrons. We say the alternating current 'passes through' the capacitor, but what's really happening is that each plate is getting charged and discharged. Capacitors store energy in the electric field set up between the oppositely charged plates. The dielectric also stores energy because the charge distribution around the atoms is distorted by the electric field. An inductor is just a coil of wire wound on a core. It's an electromagnet and stores energy in the magnetic field produced. With DC it's no different to passing a current through a length of wire - the magnetic field irrelevant (except for a short time when the current is turned on or off). So it's a short circuit. With an alternating current, the magnetic field is repeatedly created and collapses; this gives rise to the inductor's impedance.
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