How do microwaves heat up food?

In Physics by Mystifact

There is no better feeling than putting leftover pizza in the microwave. In a matter of seconds, it heats it up for you to perfection… but how? What is going on in the chamber of the microwave that allows it to give food heat and how does it happen so quick?

A microwave emits waves called microwaves. It contains 3 main components:

  1. A magnetron: this is a vacuum tube that generates the microwaves which provides energy to heat food.

  2. A waveguide: these are guides located as holes in the walls of the microwave when you open the door and look inside – they direct the waves produced by the magnetron into the chamber.

  3. A chamber: its job is what you expect; it is the container of the radiation and food – it maintains a good level of safety at all times.

How do these 3 components work together to make a microwave? Let’s define heat on a molecular level.

Heat is the transfer of energy due to a difference in temperature. At a molecular scale when molecules begin to heat up they vibrate more vigorously. This increased intensity of vibration is observed as a rise in temperature.

NOTE: heat can only travel from hot to cold.

When an oven or a stove are used to cook, the food is usually put on a heat insulating pan. This absorbs the heat, which then passes it on to the outside layer of the food. This cooks the outside of the food first, and as more heat energy is supplied, heat from the cooked parts are passed on to the neighbouring uncooked parts; heating the food from the outside to the inside.

What is the key difference with using a Microwave?

The difference between using an oven, and a microwave, is that food is cooked simultaneously throughout; but how?

Our food is filled with water – even dry foods contain some sort of moisture. Water molecules are also polar, meaning they are charged with one end being positive and the other being negative. To give these molecules more energy, we expose the food with electromagnetic waves which are produced by the magnetron (microwaves).

Electromagnetic waves are two waves in 1; one is magnetic and the other is electric, which travel perpendicular to each other at all times (demonstrated below).

In a microwave, the magnetic and electric fields of the microwaves switch rapidly. Imagine the blue wave becoming the red wave, and vice versa, very rapidly, on the animation above. In fact, they switch at a mind blowing 2.5 billion times a second.

The water in the food then tries to align with the electric field which is rapidly changing. This causes the water molecule to vibrate rapidly and due to molecular friction, heat is produced, thus heating up our food (recall definition of heat from above).

In conclusion, a microwave heats up food a lot quicker than an oven, as the food is heated inside and out simultaneously. If the food had no water, or to be more technical; no polar molecules, the microwave would pretty much be useless.

If you have any questions, leave them below and until next time, take care.

~ Mystifact

Please note; no copyright infringement is intended. All images used have been labelled for re-use on Google Images. If any artist or designer has any issues with any of the content used in this article, please don’t hesitate to contact me to correct the issue.

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