Week Seven: The Science behind Electromagnetic Waves, or How in the World Does the Radio Work?

You're driving in your car, and you turn on your radio.  Suddenly, Bruno Mars is belting out "Uptown Funk" while you dance along.  In this day and age, no one really questions if or how a radio emits the specific sounds that make up our most beloved Top 40 songs or favorite NPR talk shows, but when you think about it, the concept of radio waves, or any type of electromagnetic waves for that matter, are quite an abstract concept to think of.  Anything we see or hear relies on these strange waves that almost everyone is so familiar with but knows nothing about.  Remote sensing relies on these electromagnetic waves.  Actually, organs like our ears are really remote sensing tools that allow us to pick up sound waves.  This week, we delved into how electromagnetic waves work and allow remote sensing to be possible.

First, what is electromagnetic energy?  Also known as electromagnetic radiation, this is energy emitted in the form of waves that is released from anything over 0° Kelvin, or -273.15° C.  The sun is the main source of electromagnetic energy, but virtually everything around us emits some type of electromagnetic energy, including ourselves.  All the different types of electromagnetic energy lie on the electromagnetic spectrum, this includes the different waves we perceive, such as color and radio waves, as well as the "invisible" waves such as infrared and X-rays.

  

Source: http://butane.chem.uiuc.edu/pshapley/GenChem2/A3/3.html

 

So there are all these waves flying around us willy-nilly? No, there are rules to how these different waves act in nature.  First, each type of wave has a different period, or time it takes to go through one wave revolution (think of following the line up a hill and down a valley; that's one period).  These wavelengths are measured in nanometers.  The amount of nanometers a period tells us the frequency of a wave.  The shorter the wave, the higher the frequency.  The amplitude, or height of a wave is another defining characteristic that allows us to differentiate between types of waves. Using Planck's Radiation Law, we can find the wavelength (basically what kind of wave) emitted by a blackbody, or anything that absorbs all light that hits it then re-emits energy back (Photovoltaic Education Network).  I'm trying to keep this entry simple, so I won't explain the equation that let's us figure this out, but I'll still show it:

 

Source: http://csep10.phys.utk.edu/astr162/lect/light/radiation.html

Basically, Planck's Radiation Law (the above equation) proves that for every fixed temperature, there is a fixed wavelength (Radiation Laws).  Some other related laws that help to explain the behavior of electromagnetic radiation are the Stefan-Boltzman Law and Wein's Displacement Law.  The Stefan-Boltzman Law tells us the total energy emitted from a blackbody (Radiation Laws).  From Wein's Displacement Law, we learn that temperature and peak wavelength are proportional, because their product remains constant.  This allows us to find out the temperature of different blackbodies based on their wavelength (HyperPhysics).  

 

Source: http://csep10.phys.utk.edu/astr162/lect/light/radiation.html

 

Using all these laws, we can determine the behavior of different wavelengths across the electromagnetic spectrum.  This is important in remote sensing, because we are able to use this information to manipulate different waves.  One basic example of this manipulation is in FM and AM radio.  FM stands for "frequency manipulation" and AM stands for "amplitude manipulation."  This allows us to make certain sounds come over different channels on the radio.  Thanks to the science of electromagnetic waves, we are able to pinpoint and collect different types of data from satellites. So next time you're jamming out in your car, take a second to think about the amazing science we often take for granted in electromagnetic radiation.

Bibliography:

HyperPhysics. Ed. Carl R. Nave. Georgia State University, 2012. Web. 26 Feb. 2015. <http://hyperphysics.phy-astr.gsu.edu/hbase/wien.html>. 

Photovoltaic Education Network. Ed. Stuart Bowden and Christiana Honsberg. Arizona State University. Web. <http://pveducation.org/pvcdrom/properties-of-sunlight/blackbody-radiation>. 

"Radiation Laws." Astronomy 162. University of Tennessee, Knoxville. Web. <http://csep10.phys.utk.edu/astr162/lect/light/radiation.html>.