Why does a microwave oven heat so quickly?

Have you ever wondered why we are able to cook food so fast in a microwave oven?
Why is it so convenient in terms of time to use it instead of a classic oven?

To discover what lies in the backend of a microwave oven let’s start from its main components. This kind of oven contains three most important devices: a vacuum tube called a magnetron, which generates the energy that heats food, a waveguide hidden in the wall, to direct energy to the food and a chamber that holds the food and safely contains the radiation. The real cool stuff which is behind this revolutionary device is exactly this last one: the microwave radiation! After having been generated by the magnetron it is channeled by the waveguide and finally scattered into the main chamber of the oven.

fieldFrom a physical point of view, as all the radiations, microwaves are nothing less than an oscillating electromagnetic field, the same as light, or radiowaves.

In principle a microwave does not heat differently than any other type of heat device; at a molecular level we are dealing about an energy transfer that results in an increased motion of the molecules and eventually in a rise in temperature. Its unique feature comes as follows: in a traditional oven we heat food by placing the it inside a radiated chamber with hot walls which cause the outside of the meal to raise in temperature. The inside of the food cooks by the heat transfer taking place from the hot surface to the inside. In contrast, energy from the magnetron penetrates into the food which means that all its mass can cook simultaneously. But how does he do this?


Well our food is generally filled¬†with water which is a funny molecule positively charged at one end and negatively charged at the opposite one. To give this molecule an energy we expose it to the electromagnetic wave generated from the magnetron; this radiation stimulates simultaneously all the water molecules it encounters on its path. The typical microwave electromagnetic field oscillates 2.450.000.000 times per second. Water will try to allign with the oscillating radiation of the electric field, whose very fast variations rock the molecule back and forth rapidly. Well, imagine for a second a water molecule trying desperately to find a stable position in space being punched 2.450.000.000 times per second! That’s a big deal! The natural consequence is that the molecular friction creates heat and the frentic motion destroyes hydrogen bonds which bind molecules to its neighborhood. All this incredibly fast stuff is eventually translated into a progressive, rapid and homogeneous cooking of our food!

Cool, isn’t it?


by Francesco Pochetti