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# Electromagnetic Spectrum Activity - Microwaves

## Resources

Microwave is just another name for high frequency radio waves. Microwaves cover the range from 300 MHz - 300 GHz. A high frequency wave has a short wavelength. The relationship is defined as:

• Variables:   λ=wavelength (m)     v = speed of light (3 x 108 m/s)     f = frequency (Hz). Note 1 GHz=1 x 109 Hz
• Formula:   λ = v ÷ f
• Example:   λ = 3 x 108 m/s ÷ 100 GHz = 3 cm

Microwaves are used for Wi-fi, Bluetooth, satellite TV dishes, radar, cell phones, remote TV news trucks, GPS and microwave ovens. In nature the microwave band is 'quiet', meaning that not many sources exist for these frequencies.

Microwaves are "line of sight" meaning that they do not bend around the Earth as some longer wavelength radio waves will. The microwave antennas must be able to 'see' each other for communication to occur.

The longer the wavelength the larger the antenna must be. Your car radio needs an antenna about 18" long to pickup 1110 KHz (Whidbey Island AM radio station KWDB). Your cell phone antenna can be built into your small phone because its frequency is 800 MHz, almost 1000 times greater than the AM radio frequency! Remember that a high frequency means a short wavelength.

At the higher end of the microwave band the microwaves behave less like a radio wave and more like light. The next band of electromagnetic energy is the infrared.

There have been many concerns about the effects of microwaves on humans. After all, if microwaves can reheat my pizza what must it be doing to my brain when I use my cell phone? Microwave ovens can use 1200 watts of electrical energy to make microwaves. Your cell phone produces much less microwave power, about 3 watts. Many studies have been conducted on the health effects of microwaves on humans. The results are contradictory or inconclusive. A study in 2009 did show that accuracy and response times of cognitive functions were reduced during exposure to cell phone signals.

Nevertheless, microwaves are towards the low energy end of the EM spectrum and are considered non-ionizing radiation. Ionizing radiation has enough energy to tear electrons away from their atoms. The atoms are now 'ions'. These ions can cause unwanted chemical reactions in a material or organism.

## EM Spectrum Data Table

Name Wavelength Range Wavelength
(comparative size)
Frequency Range Energy
ionizing/ med / lo
Sources Uses
Microwaves

## Waves Glossary

Electromagnetic waves
Radiation consisting of waves of energy sent through space and matter associated with electric and magnetic fields resulting from the acceleration of an electric charge (light, x-rays, microwaves, gamma rays, etc.). 3.9
Frequency
The number of back-and-forth cycles per second, in a wave or wave-like process. 3.5
Period
The time for one wavelength to pass a point. The time for a wave to travel the distance of one wavelength. P= 1/frequency. 3.5
Wave
A rhythmic disturbance that transfers energy from place to place. 3.5
Wavelength
The distance measured from crest to crest of one complete wave or cycle. 3.5