EGEE 101
Energy and the Environment

The Microwave Oven

PrintPrint

Before we can work out how a microwave oven works, we need to know what a microwave is. The electromagnetic spectrum consists of various wavelengths of visible light (colors) as well as radio waves, X-rays, etc. There are two simple parameters that change the utility and the behavior of these various waves: wavelength and frequency. The example below uses a frequency slider to adjust the frequency/wavelength of the wave.

Temperature and Wavelengths
Click Here for a transcript.

Let’s explore a simple model of how oscillation frequency is tied to the wavelength of electromagnetic radiation.

The frequency at which electrons oscillate is essentially set by the temperature of the matter in which the electron resides. Lower temperatures yield lower frequencies of oscillation. Here, we’ve set our temperature on the low side, and you can see the molecule oscillating fairly slowly, or in other words, at a low frequency. The wavelength of the emitted radiation is also relatively long.

But, when the temperature increases, the oscillations get faster, which makes for a higher oscillation frequency. This high frequency means that the emitted electromagnetic radiation has a relatively short wavelength. For comparison again, we can decrease our temperature to watch the oscillation frequency slow, and the wavelength of the emitted radiation increase.

Credit: DMB & SS

Required Reading

NASA's web page on the Electromagnetic Spectrum provides a brief, straight-forward discussion about the topic that I expect you to take a look at. As you read, make sure you understand at least one use for each classification of wavelengths. For example, radio waves carry radio signals. What are IR and UV useful for?

After reading the NASA page, you should know that the wavelength of microwaves is about a few centimeters (cm). This energy enters the food or liquid (placed in the microwave) and excites the molecules within, causing them to vibrate more. The technical explanation is that as the molecules move more, they have more kinetic energy, which, in the case of molecules, we call temperature... thus heating up the food, very convenient.