enegry problem about microwave

Microwave is electromagnetic (EM) wave in nature. Microwave in domestic microwave oven is produced by a magnetron and emitted to the cooking chamber via a waveguide.
When the microwave hits the bread, the electric and magnetic components of the EM wave cause water molecules in the bread to vibrate vigorously. Friction between the vibrating water molecules produces heat.
In such process, microwave energy is being absorbed by water molecules at the surface of the bread, and transformed to heat energy. The heat so produced will gradually pass to the inner part of the bread by the conduction process, until the whole piece of bread is heated up.