Well, because a long time ago, I built an extremely low-power battery operated DC Tesla Coil.
It worked, but the one thing I could not figure out was why the coil with the small number of turns, the coil that typically encircles the long coil with the many turns, why this coil with smaller turns -- had to be positioned a slight distance up the many turns coil, and not either directly at its end, nor at its middle.
Well, this video, at the point I've noted, explains the answer why.
It also explains the relationship between frequency, length of resonator, and ability to create larger amplitude waves via additive superposition, that is, the ability of one wave, travelling in one direction, has the ability to add to the amplitude/crests of another wave travelling in the other direction BUT IF AND ONLY IF THEY ARE IN PROPER ALIGNMENT!
Which, incidentally, is the principle behind how a laser works (in addition to a Tesla Coil!).
Also, there's the knowledge here that we can change the frequency to match the resonating coil/cavity/resonator length/etc., OR we can change the resonator length/coil length (in a Tesla Coil this is accomplished by moving the smaller outer coil with less turns on it) to match the frequency.
So we can choose one to adjust to match what's needed by the other.
Now, if say, a Tesla Coil is storing energy when in operation by additive/constructive interference / wavefronts adding and increasing amplitude in antinode positions, then it makes me wonder if the phenomena of electronic capacitance (i.e., a capacitor, or inversely, an inductor, which is really just another form of coil) works via waves (of some sort) adding up...
Unfortunately, at this point in time, I have neither the equipment nor the knowledge nor the experience as to how to undertake such an experiment...
So, I'll leave that question for scientists or future scientists -- and/or myself in the far future (disclaimer: I am not an official "scientist" <g>) -- to answer!
