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# Electromagnetic Spectrum Activity - Radio

## Resources

The existence of radio waves were mathematically predicted in 1865, twenty years before actually discovered! The first commercial radio broadcast station started in 1920. Since then radio waves have become an crucial part of our lives. Radio waves are used in AM and FM radio, garage door openers, radio-control cars, baby monitors, television, radar, cell phones and wi-fi. In nature radio waves are made by earthquakes, lightning and objects in space such as stars.

Radio frequencies cover a very wide range, from a few hertz up to 300 GHz! For this activity the radio band covers from 3 kHz to 300 MHz. A low frequency wave has a large wavelength. The relationship is defined as:

• Variables:   λ=wavelength (m)     v = speed of light (3 x 108 m/s)     f = frequency (Hz)
• Formula:   λ = v ÷ f
• Example:   λ = 300,000,000 m/s ÷ 1,110,000 Hz = 270 m

Lower wavelengths are able to travel around the Earth better than short wavelengths. Short wave length radio waves are "line of sight". For your FM radio to receive the waves your receiving antenna must be able to 'see' the transmitting antenna.

The longer the wavelength the larger the antenna must be. The lowest radio frequencies used by man are used for communications to underwater submarines. The transmitters are huge! These antennas are over 30 miles long. Since their antennas must be smaller, the submarines can only receive. The low frequency also means information has to be sent very slowly, only a few letters per minute!

Your car radio needs an antenna about 18" long. Whidbey Island AM radio station KWDB operates at 1110 KHz. 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.

Radio waves have the lowest energy 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

## 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