Microwave ovens
Microwave ovens are a standard part of the household appliances, a kitchen can seem barren without one.
Yet how do they work, and where did the idea come from?
Let there be light
We are all familiar with light and can enjoy its beauty.
But light also has a behavior like a wave – such as ripples in water.
All light is the same, but how it reacts when encountering objects depends on its “wavelength” or distance between ripples. Here are some examples:
X-rays – Here the light has an extremely short wavelength (the ripples are very close together, about the same distance as the size of an atom).
Ultraviolet (UV) – This is the part of sunlight that gives suntans or burns. The wavelength is longer than X-rays, but still no bigger than some molecules.
Visible light – Do I really need to explain?
Infrared – This is the light given off by hot objects when you can feel the heat coming of something, but it isn't glowing.
Radio – This form of light is used for radio communication. These wavelengths can get as long as several football fields.
I left off microwaves that fit between radio and infrared light. But don't worry, we'll hear more about it.
A warm feeling inside
The story of the microwave oven begins in the 1930s.
A hot meal
It is 1933. You and friends are visiting the World's Fair in Chicago. On display are exhibits such as a history of Chicago, futuristic concept cars and a "homes of tomorrow" exhibit.
But you might also see an exhibit by Westinghouse where radio waves are being used to heat a sandwich.
To be sure, the machine packed a lot of radio wave energy into such a small space. Still, it does present possibilities. One possibility that gets explored is using radio waves to heat human tissue for medical therapy.
I see you
Now jump to the late 1930s.
The English military is concerned about a possible war and seeks a high-tech solution. A commission is selected to develop using radio waves as a death ray to knock planes out of the sky.
Surprise, surprise, they couldn't make it work.
Enter Arnold Wilkins.
Mr. Wilkins told the commission that going after a death ray was a fool's errand, but radio waves can be used to detect and determine the position of objects in the air.
Radar was born. But radar required two things.
Ordinary radio waves did not work the best, you need a light of a shorter wavelength. You need microwaves.
You need a good, strong source of microwaves so the radar can project its waves out far. The source of good, strong microwaves is a device called the magnetron.
A discovery
Now go ahead to 1945.
Percy Spencer is working with radar equipment and notices that the microwaves are melting his chocolate bars. He does some investigating and realizes that microwaves can be used to cook food.
The microwave oven was born.
Mind you, the first microwave ovens were massive. They stood 6 feet high, required a 220-volt power outlet (the same used by clothes driers and air conditioning units) and cost as much as an almost-new car.
So clearly, the technology has gotten a lot better.
A new way to dinner
So, how do they work? And how can they work so well?
In a regular oven, a heat source (heating element or burning fuel) makes the inside of the oven hot.
The heat from the oven has to work its way into the food before it can cook. This takes time. However, microwaves can go directly into the food and heat the whole thing. Much faster!
So how to make an oven that uses microwaves?
The business part of a microwave has three parts.
Oven cavity – Where the food is heated.
Magnetron – The source of the microwaves.
Waveguide – A tube for waves. Here the waveguide carries the microwaves from the magnetron to where the food is. More common waveguides for sound are stethoscopes and talking tubes.
So, what's for dinner tonight? Regardless of what is served on a plate, if a microwave is involved there is a whole lot – radio heated sandwiches, war-winning radar, melted chocolate and a whole lot of light.
On the web
A fun look into how microwaves work.
A more detailed explanation of how microwave ovens work and how the microwaves themselves heat up food.
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