Last week I microwaved some peanut butter M&Ms for 40 seconds, which is something I've done hundreds of times before to melt the chocolate on the inside. However, when I did it this time, there was some popping and then a big spark inside. There was no metal in the microwave, the bowl is microwave safe, but it did have a chip in it. I also left the M&Ms uncovered, while I usually cover them with a paper towel. Any idea what caused this? Someone elsewhere suggested this paper might be an explanation but I would think it would have happened before if that was the case.

  • Was the quantity (approximately) the same as before? – Chris H Feb 25 at 17:40
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    @ChrisH Yes, roughly a handful. – HS-nebula Feb 25 at 17:44
  • Grape is the usual object to demonstrate this effect: thenakedscientists.com/get-naked/experiments/grape-plasmas CD's and lit candles covered by glass bowls are fun as well. – Wayfaring Stranger Feb 26 at 0:53
  • @WayfaringStranger, true, and I'd think the index of refraction would be significantly different in a combination of chocolate and peanut butter than in a grape, which may not cause mostly internal reflection. Maybe the shell is made of ingredients that would cause the sparks? – HS-nebula Feb 26 at 5:47
  • @HS-nebula I think the shell is some form of hard sugar, which would be a lot different than the chocolatey innards. I Could be wrong about that, but its early right now, and I can't do a search until coffee hits. -I've never looked up the coating recipe. – Wayfaring Stranger Feb 26 at 16:28

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