[CamperBob2]

Yes, and that's precisely because they are so lossy. It's not a resonant effect. You're just taking advantage of the grape's cross section being roughly a quarter-wavelength at 2.4 GHz, which allows the magnetron to dump a ton of power into it.

It's analogous to using a couple of forks to operate a pickle from 120V.

[MacsHeadroom]

>roughly a quarter length

Is that not resonance?

[CamperBob2]

The same thing would happen with an ideal resistor whose leads formed a dipole of the right length, so no.