There are many scales to denote the Electromagnetic Spectrum. The Frequency Scale and the Wavelength Scale.

Other scales are used, such as wave number and energy. Each scale is subdivided into bands.

1 - 10^4: Long Radio Waves
10^5 - 10^6: Amplitude Modulation Radio Waves
10^6 - 10^7: Citizen Band Radio Waves
10^8: Frequency Modulation Radio Waves
10^9 - 10^12: Microwaves
10^11 - 10^15: Infrared Waves
10^15: Visible Spectrum
10^15 - 10^17: Ultraviolent Waves
10^16 - 10^19: X-Rays
10^19 - 10^23: Gamma Rays

[Editor's note (Gz), 10/4/2002: Consolidated three E1 writeups here.]

A visual representation of the electromagnetic spectrum, not completely on scale:
```                    Gamma Ray  |- 10 pm
X-Ray  |- 100 pm
violet   \                     |
(400 nm)  \        Soft X-ray  |_ 10 nm
blue       \               UV  |
green       \ ___              |- 100 nm
yellow      / --- Visible      |_ 1 µm
orange     /               IR  |
red       /                    |
(700 nm) /              T-ray  |- 100 µm
|
|_ 10 mm
Microwave  |_ 100 mm
Cell phone  |
Radio/TV  |- 1 m
```

wavelengths:
pm = picometer
nm = nanometer
µm = micrometer
Here it is, folks, the complete electromagnetic spectrum. The longest wavelength in the spectrum is 2^60 (or 1,000,000,000,000,000,000 OR about a billion billion) times as long as the shortest, and the spectrum itself is continuous. This means the names and boundaries we assign to each wave are arbitrary, merely there to help our own system of classification.

Quick note, the infrared spectrum is everything you see before visible light, and the ultraviolet spectrum is everything you see after visible light...On the chart that is.You can't actually see infrared or ultraviolet. Hehehe...

Legend:

• Bandwidth
• Where this type of wave can be found, in terms of frequency
• Where humans use this wavelength, and for what purpose

• Extremely Low Frequency (ELF
• 0 KHz to 3 KHz
• Very Low Frequency (VLF)
• 3 KHz to 30 KHz Includes:
• 9 KHz to 540 KHz
• 9 KHz to 540 KHz
• Low Frequency (LF)
• 30 KHz to 300 KHz
• Medium Frequency (MF)
• 300 KHz to 3000 KHz Includes:
• 540 KHz to 1630 KHz
• Traveller Information Service
• 1610 KHz
• High Frequency (HF)
• 3 MHz to 30 MHz Includes:
• 5.95 MHz to 26.1 MHz
• Very High Frequency (VHF)
• 30 MHz to 300 MHz
• Low Band: TV Band 1 - Channels 2-6
• 54 MHz to 88 MHz
• 88 MHz to 174 MHz
• High Band: TV Band 2 - Channels 7-13
• 174 MHz to 216 MHz
• Super Band (mobile/fixed radio TV)
• 216 MHz to 600 MHz
• Ultra-High Frequency (UHF)
• 300 MHz to 3000 MHz Includes:
• Channels 14-70
• 470 MHz to 806 MHz
• L-band:
• 500 MHz to 1500 MHz
• Personal Communications Services (PCS)
• 1850 MHz to 1990 MHz
• Unlicensed PCS Devices
• 1910 MHz to 1930 MHz
• Superhigh Frequencies (SHF) (Microwave)
• 3 GHz to 30.0 GHz Includes:
• C-band
• 3600 MHz to 7025 MHz
• X-band:
• 7.25 GHz to 8.4 GHz
• Ku-band
• 10.7 GHz to 14.5 GHz
• Ka-band
• 17.3 GHz to 31.0 GHz
• Extremely High Frequencies (EHF) (Millimeter Wave Signals)
• 30.0 GHz to 300 GHz Includes:
• Additional Fixed Satellite
• 38.6 GHz to 275 GHz
• 300 GHz to 810 THz
• ### Visible Light (everyone's favorite)

• 810 THz to 1620 THz
• 1.62 PHz to 30 PHz
• X-Rays
• 30 PHz to 30 EHz
• Gamma Rays
• 30 EHz to 3000 EHz

Some of this I got from Mr. Isaac Asimov's Fantabulous book The Universe: From Flat Earth to Black Holes and Beyond. I love him, and you will too... oh yes, you will...

Amongst the different ways that the electromagnetic spectrum can be classified, one of the easiest, at least to me, is to measure it in electronvolts. This is especially true of photons that are going to interact energetically with ordinary matter, which is usually visible light and above. An electronvolt is the amount of kinetic energy that an electron gains when propelled by a field of one volt, or conversely the amount of kinetic energy needed to push an electron against a field of one volt. It is possible to imagine a photon as striking an electron, and if the photon is energetic enough, pushing the electron against an electric current, or out of an energetically favorable situation, such as a comfortable orbit in an atom.

This is helped along by the fact that in the range of visible light, the numbers connect somewhat to a scale we might be familiar with. The equations are rather complicated, and I can't claim to understand them totally, but by taking this equation, and multiplying it by the speed of light, we get an equation where 1240 nm=1 ev, and where moving down in wavelength gives you a corresponding increase in energy. If the analogy is not too anthropomorphic, an electron volt is about equal to one dollar. Most common chemical interchanges is in the region of a few electron volts, just as dollars are our common walking around money. Ultraviolet light is in the 10-100 electronvolt range, making it something like large purchases, but not too unusual. Above that, we get into X-Rays and gamma rays, with electron volts anywhere from thousands to millions. And much like with money, you don't see that amount floating around casually very often. Also, the first ability for a photon to engage in pair production occurs around one million electron volts, which makes sense...you would have to be a millionaire to afford something as exotic as antimatter.

Although my hastily sketched comparison chart of electronvolts with dollars is somewhat whimsical, the important thing is to remember that electronvolts are a permissible, and sometimes very useful way to measure the energy of a photon.

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