Question: What is the Operating/Working Principle of a Microwave oven?

Microwaves   are high-frequency electromagnetic waves; the energy released food to be cooked or reheated without       changing either the form or the color.
   
    Cooking Principle :
   
    a). The microwaves generated by the magnetron reflected cavity and are   distributed uniformly as the food rotates on       the turntable. The food is thus   cooked evenly.
   
    b). The microwaves are absorbed by the food up to a depth of about 1 inch   (2.5 cm).
   
    Cooking then continues as the heat is dissipated within the food.
   
    c). Cooking time varies according to the container used and the properties   of the food like:
   
        i) Quantity and Density 
   
        ii) Water Content
   
        iii) Temperature