Imagine a simple setup. I have a copper disc and another copper element held close to the disc at one of it's sides, this element is stationary but the disc is rotating, the part between the disc and the element that overlaps forms a capacitor. If I put a potential difference (voltage source) across the rotating disc and stationary element the capacitor charges up.

For the stationary copper plate everything is clear but the disc is rotating does that mean that the charge buildup on the disc that faces the charges on the stationary plate are constantly moving their position on the disc surface in order to always be at the position that faces the plate because the E field attracts them there? So even the disc is rotating the charges are moving on the disc surface to stay in a stationary position with respect to the physical disc rotating?

  • $\begingroup$ I think that would be true but for the charges to move resistance would be encountered and there is some energy loss. $\endgroup$ – PhysicsDave Dec 23 '18 at 14:18
  • $\begingroup$ sure resistance comes into play for any room temp conductor, here I mostly desire to know how the charges would move on the disc surface in order to preserve the capacitor. $\endgroup$ – Girts Dec 23 '18 at 15:25
  • $\begingroup$ can anyone please answer this questions in general? thanks $\endgroup$ – Girts Jan 1 '19 at 18:29
  • $\begingroup$ Yes I would agree the charges would be moving because the E field attracts them to the stationary plate, electrons do have a drift velocity so they may have trouble keeping up in the wheel is to fast, in this case the charge cloud would be spread out a bit more. $\endgroup$ – PhysicsDave Jan 1 '19 at 22:02

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