How Microwaves Heat Your Food

published Apr 18, 2015
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(Image credit: Emma Christensen)

Microwave ovens seem almost magical because they can heat leftovers in just a couple of minutes (in seconds, even), when a conventional oven would take 20 minutes or more.

But the technology that goes into microwave ovens isn’t actually magic, but science, practically applied and intelligently designed. Here’s how they work.

The Parts of a Microwave

The microwave oven is made from a few key pieces:

  • Transformer: This converts the electricity from the wall socket to a higher voltage.
  • Magnetron: This converts that electric current to microwaves. A microwave is essentially an electromagnetic wave of energy with a wavelength that is longer than infrared radiation, but shorter than radio waves — or in other words, microwaves have a lower frequency than infrared radiation and higher frequency than radio waves.
  • Mesh: A special mesh covers the door and the surrounding walls and allows the microwaves to bounce back and around within the microwave oven box.

The Key Is Polar Molecules in Foods

Polar molecules, like water, which have a partial negative charge on the oxygen and a partial positive charge on the hydrogen atoms, move and rearrange to orient themselves according to the wave of radiation that is alternating.

That motion, stimulated by the microwave oven’s microwaves, produces heat and collisions that transfer that energy throughout the food.

Advantages to Microwave Ovens

The beauty of this heat source is that the microwaves are not heat per se, but rather they induce tiny movements that generate heat in the food itself, and not in the surroundings. The heat is then conducted throughout the food.

Also, microwaves are able to penetrate through thicker layers of food (around 1 1/2 inches) much better than the hot air of your oven. In regular ovens, the heat is conducted from the outermost surface towards the inside.

Disadvantages to Microwave Ovens

Foods can dry out from rapid heating, and browning meats isn’t really possible.

Side note about microwave safety: Please don’t fear the microwave oven. Microwave ovens are built with a metal frame inside in order to contain microwaves within the oven box, and the window is lined with a mesh to reflect microwaves without letting them pass through. Basically, don’t worry about standing too close to a microwave.

Do you use a microwave oven to cook foods or reheat leftovers?