How Do Microwave Ovens Work? Microwave ovens work by exciting the food’s liquid molecules, producing thermal energy, or heat, ultimately cooking the food. The principle behind this involves microwaves, a type of electromagnetic radiation produced by a magnetron within the appliance, and dielectric heating. Thus, microwave ovens work best using foods with high moisture or fat content.
Jump Ahead
- What Are Microwaves?
- How Do Microwaves Work in the Oven?
- How Do Microwaves Stay Inside the Appliance?
- How Do Microwaves Cook Food?
- All This Science Is User-Friendly
- Resources
- Glossary of Terms
- Expert Opinion
What Are Microwaves?
Microwave ovens are so named because they use microwave radiation for cooking food. Microwave radiation is a form of electromagnetic radiation with a frequency of 300 MHz to 300 GHz. These wavelengths are much shorter than radiofrequency waves and must travel in a straight line, so due to the Earth’s curvature, they are useful only up to thirty feet. This limits their use to transmitting data between ground stations or nearby satellites. They are also used in radar technology and microwave ovens. [1][2]
How Do Microwaves Work in the Oven?
A high-voltage power source powers microwave ovens. This energy is transferred to a magnetron, a device that converts electric energy to microwave radiation. The radiation then passes through a waveguide that controls the microwaves’ direction and sends them into the cooking chamber. The microwaves are reflected off the interior of the appliance’s metal walls and form standing waves, passing through the food to heat it. A turntable will move the food through the waves to distribute hotspots that can form in the standing waves. [3]
How Do the Microwaves Stay Inside the Appliance?
The microwave oven unit works on the principle of a Faraday cage. A Faraday cage is intended to block out all electromagnetic radiation present in the atmosphere, such as radio waves, and confine other waves inside the unit. Microwaves cannot penetrate metal and are instead reflected off. This is why microwave ovens are made of metal. All microwave parts must be covered in metal, including the mesh-covered glass door and light bulb cavity, for this principle to work. [4]
How Do Microwaves Cook Food?
Some falsely believe that food is chemically altered when heated by microwaves. Microwave cooking is actually a simple process of exciting molecules to create heat.
The food contains molecules with dipoles, that is, positive and negative poles. The microwaves change the polarity of the field, causing the molecules to flip continuously, creating friction. This friction creates heat, which cooks the food item and is known as dielectric heating. Microwaves primarily work on the water molecules present in foods because they most efficiently absorb microwaves. [5]
All This Science Is User-Friendly
Microwave ovens utilize mechanical or electronic mechanisms to control power output, time, safety, and user interface. In modern appliances, this interface is almost always in the form of user-friendly buttons and LED displays positioned conveniently on the front of the microwave oven. These devices allow the user to safely and easily adjust the cooking process without exposing themselves to the inherent dangers of manually manipulating the circuitry of the magnetron and its electric power supply.
Resources
[1] Occupational Safety & Health Administration – Radiofrequency and Microwave Radiation
[2] University of Mississippi – Communications-Communication Channels-Microwaves/Satellites
[3][4] Vollmer, Michael. “Physics of the Microwave Oven.” Journal of Physics Education, Vol. 39, No. 1, 2004. print
[5] Penn State News – Probing Question: How Do Microwaves Cook Food?
Glossary of Terms
Dielectric heating: method by which the temperature of an electrically nonconducting (insulating) material can be raised by subjecting the material to a high-frequency electromagnetic field.
Encyclopedia Britannica
Electromagnetic radiation: is a form of energy that is produced by oscillating electric and magnetic disturbance, or by the movement of electrically charged particles traveling through a vacuum or matter.
University of California, Davis
Expert Opinion
“Simple estimates easily show that the number of microwave photons within a commercial oven is orders of magnitude too small to establish multiphoton dissociation or ionization. One may therefore conclude that the food cannot be altered chemically while heated in a microwave oven.”
Michael Vollmer Physics of the Microwave Oven
“Although technically microwaves are a kind of electromagnetic radiation, we shouldn’t use the word ‘radiation’ to describe them—it scares a lot of people unnecessarily.”
Swamy Anantheswaran, Penn State professor of food science
