# Does a charged capacitor weigh more than uncharged? [duplicate]

I know that charging a capacitor only moves particles from one plate to the other, so the total amount of charge in the capacitor does not change, nor does the total number of particles.

However, the charged capacitor does have electrical energy that the uncharged capacitor does not have, and energy has a mass equivalence according to $$e=mc^2$$, so wouldn't the capacitor weigh a little bit more when charged?

A 470 μF capacitor charged to 3.3 V, for instance, would have a stored energy of 2.6 mJ, which has a mass equivalence of 0.03 femtograms, which is the weight of ~1,416,666 carbon atoms?

Likewise, a superconducting loop inductor would weigh slightly more when it is energized (has a current flowing through it) vs unenergized because of the mass equivalence of the energy stored in the magnetic field?

• physics.stackexchange.com/a/466278/176 Jun 10, 2020 at 14:46
• why do you doubt your calculations ? The football example is not the same. It depends on the inertial frame, whereas what you calculate does not. Jun 10, 2020 at 15:02
• @annav Because of the comment that I linked to Jun 10, 2020 at 15:35
• I had read the question. only. With special relativity any stored energy in principle should show. Think of it as the difference in the individual four vectors making up the capacitor plates, adding up to a change in the invariant mass. Jun 10, 2020 at 18:18