I disassembled an iPod Nano 2 yesterday and was surprised to find a round brass-coloured plate glued to the back. I didn't find any mention of it at the teardown over at ifixit.com, as they didn't cut the case in half. The back of the logic board has two contacts pressed against this plate.
Since it just seems to be a piece of metal connected to the case and is quite discoloured, I'm reminded of galvanic anodes attached to chips to protect them from corroding. Does anyone know why this plate is there?
I'm a physics teacher and this seems like an opportunity to teach my students something.