### Graph the Electromagnetic Spectrum - Lesson Idea

Radio Stations and the EM Spectrum

Most students know the call numbers of their favorite radio stations, but they probably don't realize what those numbers mean.  Each number is actually the frequency of the radio waves that the station uses to transmit its signal.  After doing these exercises, students should have a deeper understanding of how the electromagnetic spectrum is part of nature and is utilized by human beings for modern technology.

Lesson Steps:

1. With your class, make a list of all the radio stations and their numbers on the dial, separating AM and FM (e.g.. KGO 810 AM, KFRC  99.7 FM.).  AM stations are measured in kilohertz, FM stations are measured in megahertz.  If you need more information on local radio stations, try the Yahoo search engine link:  http://dir.yahoo.com/News_and_Media/Radio/Stations/
2. Have your students make a graph of the stations by frequency.
3. If appropriate to the level of your students, teach them the math which relates frequency to wavelength:

frequency x wavelength = 300,000 kilometers/second (speed of light)

wavelength = 300,000/frequency

example: 810 AM

810 kHz = 810,000

300,000/810,000= 0.37 km = 370 meters

So, 810 AM transmits on waves that are almost four football fields long!

If the math isn't appropriate, students could still be shown that wavelength and frequency are inversely related: the longer the wavelength, the lower the frequency and vice-versa.

4. Discuss with the class how changes in the waves to higher frequencies (shorter wavelengths) seems to change the properties of the waves.

Some familiar forms of electromagnetic radiation:

VCR remote controls, electric heaters - infrared
TV, cellular phones and pagers - radio (different frequencies than AM and FM)
Microwave oven - microwaves
Sun screen - protects skin from ultraviolet light
Candles, light bulbs, lasers - visible light
Medical and dental X-rays - X-rays

After doing the above activities, the frequencies/wavelengths of other parts of the spectrum should make more sense to students.  For example, the wavelengths of the X-rays and Gamma rays that RHESSI will use to make pictures of the sun are smaller than the diameter of an atom.

Student Project Ideas:

1. Research the radio band of the electromagnetic spectrum to learn which wavelengths are used by different forms of communication (cellular phones, global positioning system, emergency, military, aviation etc.).  This is an important political topic as more and more parts of a limited spectrum are needed by modern communications systems.
2. Research what it is that is special about the light produced by a laser?
3. Research the history of X-rays, including their discovery and use.