Microwaves as they are reflected off the metal sides of the oven cavity (8)
Once the power is turned on energy is provided to the system which causes the wave guide transfers electromagnetic energy, RF energy, into the oven cavity from the magnetron. The electromagnetic energy flows throughout the oven cavity bouncing off the metal walls until it is absorbed by the food. Heat is the transfer of energy there are three different means of energy transfer conduction, convention, and radiation. Conduction is energy transfers through direct contact, convection is heat transfer within a fluid, and radiation is transfer from waves. Since the microwaves are absorbed by the food the heat is transfer by radiation, which causes the food to vibrate, as the food vibrates it interacts with other molecules, causing friction between molecules as they move, this friction heats the food up. The air around the food doesn't heat because the molecules in air have a lot less friction then the food does. Most containers used to store food allow the microwaves to pass through easily, however metallic bowls and foil reflect the microwaves. The metallic objects inside the oven cavity will frequently act as a conductor for the electric charges which can cause arcing to occur between the metal sides of the oven cavity and the metal object inside.
