Microwave heating is more efficient on liquid water than on fats and sugars (which have a smaller molecular dipole moment), and also more efficient than on frozen water (where the molecules are not free to rotate).[6]  Microwave heating is sometimes explained as a resonance  of water molecules, but this is incorrect: such resonance only occurs in water vapor at much higher frequencies, at about 20 GHz.[7] 
http://en.wikipedia.org/wiki/Microwave_oven#Principles

Molecular rotation  occurs in materials containing polar molecules having an electrical dipole moment, which will align themselves in an electromagnetic field. If the field is oscillating, as in an electomagnetic wave, these molecules rotate to continuously align with it. This is called dipole rotation. As the field alternates, the molecules reverse direction. Rotating molecules push, pull, and collide with other molecules (through electrical forces), distributing the energy to adjacent molecules and atoms in the material. Temperature is the average kinetic energy (energy of motion) of the atoms or molecules in a material, so agitating the molecules in this way by definition increases the temperature of the material. Thus, dipole rotation is a mechanism by which energy in the form of electromagnetic radiation is converted to heat energy in matter.
http://en.wikipedia.org/wiki/Dielectric_heating#Mechanism

kayaknya sih pemancarnya ga bergerak. tapi alasnya yang bergerak.
nih saya nemu link vidoe2 tentang benda2 yang jangan dimasukan kedalam microwave:
http://www.kaskus.us/showthread.php?t=3585935

kalau dari video itu benda yang ga ada airnya pun bisa meledak dalam microwave.
gimana tuh bisa dijelaskan teori dari video2 tersebut?