My plate broke, someone explain ?

Glass will expand when heated. Microwaves do not heat glass, but only water. They heat your sub by heating the water in it. The heated sub sits in contact with the unheated plate, heating only the portion under the sandwich. That part tries to expand, but has to push on unheated parts of the plate. It can't, so it shatters.

Did your glass plate have any small cracks? Maybe water got in them, you put it in the microwave, started it for a few minutes, then the water molecules started vibrating (microwaves target water particularily), getting hotter, and water expanding, but since there was no where for it to expand, the crack got bigger/plate "exploded", and eventually you took it out, asked us, and I replied.

I can't really tell more from what you've said, but that is one of the possibilities.

Hope you have a backup plate so you can eat,

Mulhaq_2005

Its because ur glass plate couldn't anymore counteract the hotness of the microwave.

Your microwave was touched by a noodly appendice, you should keep the glass you are blessed.

well maybe the hot and (maybe) cold of the sub colided and cause a breaking but what do i know?