Question

When I heat water in a cup in a microwave, why does the top half of my cup become hot whereas the bottom half remain the same?

Answer 1

well it is property of liquid or any fluid that hot part always rises up, like hot air rises up in the atmosphere, similarly as soon as the water at the bottom gains energy it rises up , therefore the bottom half remains slightly colder to that of upper half.

Answer 2

and upper half which is hot, rises up

Answer 3

Agreed. But, a microwave provides uniform EMW Microwave radiations.
then why should there be a hot part and cold part in the liquid at the same instant.
Even then, why is the observed difference between the temperatures so high?

Answer 4

see if you are providing heat from every direction then still think that in the mid region it contains a bit colder quantity that will surely fall down and lifting up the hotter area.