The Electromagnetic Spectrum

“Light” is what we call the special waves that our eyes can detect.  All light waves are really waves with two parts – a vibrating electric field and a vibrating magnetic field (we’ll discuss these later).  For now, realize that being an electromagnetic wave is what makes light so special. 

• Light travels really, really fast.  It travels at 300,000,000 meters every second!  That’s the same as 185,000 miles every second.  Sound doesn’t travel very fast at all, compared to light – only about 340 meters every second.  The next time there is a thunderstorm, look for this:  when the storm is farther away, you see the lightning way before you hear the thunder.  When it is closer, the lightning and the thunder appear to happen at about the same time.
• Because light is a wiggle of electric & magnetic fields, it can travel through empty space.  Remember the three processes of heat transfer?  Only light & heat radiation can get to us from the Sun, because outer space is (mostly) empty.  We don’t get any heat or light from the Sun by conduction or convection. 

Light is special because we can see it.  But there are other electromagnetic waves that travel at the same fast speed of 300,000,000 m/s that we can’t see.  The different portions have different names, mostly based on how they were discovered.  The main difference between the sections is their wavelength.  (Remember, the shorter the wavelength, the higher the frequency.  And, for electromagnetic waves, the higher the frequency, the more the energy).

• Radio waves – wavelengths from about 10,000 meters to about 10 centimeters.  These pass through you all the time without any effect.  Your cell phone uses radio waves.
• Microwaves – wavelengths from about 10 centimeters to about 0.1 millimeters.  Most of these pass through you without any effect.  A very special microwave, with frequency about 2.45 Gigahertz (wavelength 12.2 cm) is used to heat water and other materials in a microwave oven.  Most other frequency microwaves would not cause you any harm.
• Infrared – wavelengths from about 0.1 millimeters to about 700 nanometers.  This is divided into two sections, near and far.  Far infrared, the longer wavelengths are detected by your body as heat (this is heat transfer by radiation).  Near infrared, the shorter wavelengths, are not detected by your body, but are used by remote controls (like for your TV).
• Visible light – wavelengths from about 700 nm to about 400 nm.  This is the very narrow section that we can see with our eyes.  The 700 nm end corresponds to the color red (and so the region of longer wavelengths is called infrared), and the colors follow in rainbow order:  orange, yellow, green, blue to violet at 400 nm.
• Ultraviolet – wavelengths from about 400 nm to about 1 nm.  These are just shorter than visible light (and notice the name, ultraviolet).  These start to have energies that can damage us; though we can’t see these waves, they cause sun tans, sun burns, and skin cancer.
• X-rays – wavelengths from about 1 nanometer to about 10 picometers.  These have such short wavelengths that they are absorbed by some of your larger atoms, such as the calcium in your bones.  They pass right through soft tissues (made up of smaller atoms – carbon, oxygen, hydrogen…), which is how we get those cool pictures.  These can do damage, and so your doctors will try to limit the number of X-ray pictures they take of you.  X-rays have the most potential to harm your offspring, not you, by damaging your sex cells (eggs, sperm).  This is why you always get a lead shield over your torso when you have a dental x-ray.
• Gamma-rays – wavelengths shorter than 10 pm.  These are the shortest wavelengths and the highest energies.  Gamma-rays can damage individual cell structures, like your mitochondria (that produce energy for the cell).         

Name: ___________________________           Date: __________________      Period: ________

The Electromagnetic Spectrum

• List the seven sections of the spectrum in order from longest to shortest wavelength.
  
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• Which section has the lowest frequency? _________________________________________

• Which section has the highest energy? _________________________________________

• Which color of light has the highest frequency? ____________________________________

• Which color of light has the lowest energy? _______________________________________

• Which has a longer wavelength – radio or infrared? _________________________________

• Which has higher energy – ultraviolet or microwaves? _______________________________

• Which has a higher frequency – visible or x-rays? __________________________________

• Would it be correct to say that infrared is just a lower frequency light wave?  Why? 
  
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• Are radio waves and sound waves basically the same, or very different?  Explain.
  
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