Also, the soup on the outside is thinner so it's going to get heated from all directions. The soup on the outside is essentially getting more microwaves than the soup in the middle, so it gets hotter.
Why does the outside of a bowl of soup get hot? Heat transfers from the soup to the bowl trough conduction because they are directly touching. ... Radiation transfers heat to the pavement through empty space. Because the pavement is black, it absorbs more heat
