How Microwaves Work

When we think about heat used for cooking, we think about fire, or at least heat that we can both see and feel.  But when it comes to microwaves, the only evidence of heating taking place is the fact that our food is hot.  And this leads many of us to wonder just how microwaves are able to heat our food.

You might be surprised to learn that the same type of waves that bring you music in your car and your home are used by microwaves to produce heat.  Yes, believe it or not, microwaves use radio waves to cook your food.  And, as the name would imply, these waves are micro in size when compared with the waves used to transmit sound.

But your food doesn’t heat up when standing next to a radio, so you know something else is going on here.  What is the difference?

First of all, the radio waves used in a microwave are both targeted and contained within the microwave itself.  These microwaves are about 12 centimeters long, which means their ability to travel is limited, and the metal casing of the microwave prevents them from escaping.  Within their contained environment, these waves agitate the water molecules in food, causing them to vibrate.

As these vibrations occur, the water molecules rub against each other.  This contact generates friction, producing the heat that ultimately cooks your food.

So, now we know how the heat used in microwaves is different from other sources of heat.  Our next step is to understand exactly how the microwave produces and utilizes these heat-producing waves.

1. First, as you know, a power source is needed. Microwaves use the typical household power of 120 volts.
2. The transformer inside the microwave then converts the 120 volts into 4,000 volts or more, depending on the model of the microwave.
3. This high voltage is then used to power an element called the magnetron, heating a filament at its center.
4. This filament boils off electrons which then are spun using two ring magnets; this generates the microwaves.
5. An antenna is then used to direct the microwaves from the area where they are generated into the food compartment. This is also called a wave guide.
6. The microwaves then bounce around the inside of the microwave, penetrating the food and agitating the molecules, producing heat.
7. The metal, including the mesh on the door, keeps the waves contained while the turntable ensures that the food heats evenly.

Wondering how cooking in a microwave differs from cooking in conventional ovens?  In short, it is the difference between conduction and radiation.

Conduction cooks from the outside in, heating the external parts of the food—usually the bottom—and that heat then slowly transfers to the inside of the food, eventually heating and cooking it.  So does that mean that microwaves—which are a form of radiation—cook from the inside out?

Not exactly, as that would mean that microwaves simply do what conventional ovens do in reverse, and if that were the case, they wouldn’t actually heat food any faster.  Instead, microwaves are cooking all parts of the food simultaneously, which results in rapid cooking time and more even cooking.

However, microwaves do target water molecules.  So if you are cooking or heating a food item that has layers or multiple components, the part with more water molecules will heat faster than the other parts of the dish.  A great example of this would be a bread bowl with soup in it; since the soup has more water, it will heat faster than the bread will.

By now, you are probably familiar with a few of these, but others will likely come as a surprise.  Below are items that people commonly put in the microwave that shouldn’t be placed in there.

• Chinese-Style Take-Out Containers: By now, we all know that we should avoid putting metal in the microwave; the metal can gather volts, producing harmful gases and, potentially, fire. However, most people forget about the metal handle on their take-out containers.  Also, be mindful of aluminum foil, which is a major hazard when placed inside microwaves.
• Paper Bags and Newspaper: If the paper was not made to be placed in the microwave, heating it inside of one can produce toxic fumes. And, much like metal, they can catch fire.
• One-Time-Use Containers: While it is tempting to be thrifty, your butter, yogurt, and other plastic containers are not designed to be used in the microwave. Doing so can cause them to melt and allow chemicals to seep into your food.  The same applies to Styrofoam.
• China with Metallic Trim: Again, we know that metal and microwaves are a bad combination, but this is easy to miss. Another commonly missed item are travel mugs with metal lining.  Be sure to check before you microwave.
• Any Plastic NOT Marked “Microwave Safe”: We already covered one-time-use plastic containers, but there are also reusable containers that cannot be placed inside the microwave. If it is plastic, always check the bottom to see if you can heat it in the microwave.
• Nothing: If you turn on the microwave without anything inside of it, there is nothing to absorb the waves. This means the elements of the microwave itself will absorb them, and it will quickly self-destruct.

Due to a lack of understanding regarding how microwaves work, many people are concerned about how microwaves can harm them.  Below we are going to debunk a few of these misconceptions.

• Microwaves Cause Cancer: Because microwaves are so short, their particles simply do not have the power to cause damage to cells.
• Microwaves Cause Plastics to Seep Chemicals: The efficient nature of microwaves means that their radio waves pass harmlessly through plastics and other materials. Yes, you do need to use microwave-safe plastics, but as long as you do so, you will be fine.
• Microwaves Can Burn You: While the food can be hot enough to splatter and burn you, the microwave itself will remain cool, so you can reach in without risk of burning yourself.

Hopefully, we have helped take some of the mystery out of this kitchen device.  Have any unanswered questions?  Ask us in the comments!