Information in Radio Waves
Background: Electromagnetic Spectrum
According to the equations developed by James Clerk
Maxwell in the 1860s on electromagnetism, the predicted
speed of electromagnetic waves roughly equaled the
“known” value for the speed of light. From this relation, it
was inferred that regular light must be a type of
electromagnetic wave. Maxwell’s equations also
predicted than an infinite number of frequencies could
exist and therefore was the first to hint at an entire
electromagnetic spectrum outside of just visible light.
Despite no real explanation for them, other types of light
were discovered long before the entire spectrum was
alluding to by Maxwell. In 1800, William Herschel was
testing the temperature differences in the different colors
in diffracted light. When he moved the thermometer
beyond the red end of the spectrum he noticed that the
temperature rose to its highest point. From this he
reasoned that an invisible form of light must exist and
named them calorific rays. A year after infrared light was
discovered, an invisible form of light was discovered at
the other end of the spectrum. A scientist named Johann
Ritter reasoned one must exist due to the polarity of
nature. The focus of his experiments with light were the
chemical decomposition of silver nitrate, a substance
known to react with light. By testing the decomposition
of the substance in different colors of light he found that
violet light caused faster reactions than red, and the
fastest rates of decomposition existed beyond visible,
violet light. This form of light was was named chemical
rays but they were later renamed to ulraviolet light.
Maxwell’s equations essentially paved the way for the
understanding and discovery of the rest of the spectrum.
In 1886, Heinrich Hertz successfully generated waves in
what we know as the radio portion of the spectrum. Not
long after in 1895, x-rays were discovered in an experiment involving an evacuated tube
exposed to high voltage. Five years later, originally thought to be particle emissions, Gamma
rays were discovered. While overall important, the discovery of the invisible portions of the
spectrum pale in comparison to the overall utility that followed. Scientists, from Maxwell’s
equations, reasoned that they should be able to detect this invisible radiation from cosmic
sources, paving the way for radio astronomy as we know it today. It was also recognized that
these electromagnetic waves, if possible to be produced shown by Hertz, should be able to be
manipulated to carry information. Paving the way to modern technology.
Information in Radio Waves
Reference:
"Electromagnetic Spectrum." - Introduction. Web. 13 July 2014.
<http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html>.
"The Electromagnetic Spectrum." Electromagnetic Spectrum. Web. 15 July 2014.
<http://imagine.gsfc.nasa.gov/docs/science/know_l2/emspectrum.html>.
"Herschel Discovers Infrared Light." Herschel Discovers Infrared Light. Web. 15 July 2014.
<http://coolcosmos.ipac.caltech.edu/cosmic_classroom/classroom_activities/herschel_bio.html>.
"Introduction to the Electromagnetic Spectrum and Spectroscopy." PharmaXChangeinfo Introduction to the Electromagnetic
Spectrum and Spectroscopy Comments. Web. 15 July 2014. <http://pharmaxchange.info/press/2011/08/introduction-to
the-electromagnetic-spectrum-and-spectroscopy/>.
"Molecular Expressions: Science, Optics and You - Timeline - Johann Wilhelm Ritter." Molecular Expressions: Science, Optics and
You - Timeline - Johann Wilhelm Ritter. Web. 15 July 2014.
<http://micro.magnet.fsu.edu/optics/timeline/people/ritter.html>.
Standards:
HS-PS2-5
Plan and conduct an investigation to provide evidence that an electric current can produce a
magnetic field and that a changing magnetic field can produce an electric current.
HS-PS4-1
Use mathematical representations to support a claim regarding relationships among the
frequency, wavelength, and speed of waves traveling in various media.
HS-PS4-3
Evaluate the claims, evidence, and reasoning behind behind the idea that electromagnetic
radiation can be described either by a wave model or a particle model, and that for some
situations one model is more useful than the other.
HS-PS4-4
Evaluate the validity and reliability of claims in published materials of the effects that different
frequencies of electromagnetic radiation have when absorbed by matter.
Enrichment:
- http://www.youtube.com/watch?v=lwfJPc-rSXw
5 minute video on the EM spectrum by NASA
- Simple Demonstrations / Labs:
-http://coolcosmos.ipac.caltech.edu/cosmic_classroom/classroom_activities/
ritter_example.html
-http://coolcosmos.ipac.caltech.edu/cosmic_classroom/classroom_activities/
herschel_xample.html
Recreate the discoveries of Herschel and Ritter
- Great website:
- http://coolcosmos.ipac.caltech.edu/cosmic_classroom/
multiwavelength_astronomy/multiwavelength_astronomy/activities.html
Unit Breakdown:
This unit is designed to give students a basic understanding of the electromagnetic spectrum and the
basic properties of it. Included is a powerpoint presentation along with an accompanying “Teacher’s
Notes” to guide you in use of the slides if needed. Various assessments have also been included that
align to this unit. One that supplements the presentation, one that has students manipulate basic light
speed equations, and one that serves as an end of unit test or quiz. Lastly, a basic lab activity has been
included that investigates the properties of refraction and scattering of visible light waves. As with all of
these units, you are free to use and change any parts of these materials provided.