Ian,
Thats great, thanks.
I have heard that this works as well on the HOT side. If you get a very clean cup and put pure water in it, then microwave it for several minutes..................
Without impurities like dust particles for the water to coalesce around it will not boil.
But put a tea bag, some sugar or even a spoon in it and it will explode into a boil!
Please be very very careful if you try this, as boiling water can erupt all over.