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The Electromagnetic Spectrum of Radiation

The EM spectrum explained.
Bandwidths, wavelenghts, frequencies. Measuring units. Use in analytical spectroscopy. Commercial and wireless applications.

The EM spectrum of Radiation Bands, Wavelenghts and Frequencies

The Electromagnetic Spectrum of Radiation

All of these waves are electric and magnetic forces - forces which vary with time in direction and intensity. All have speed 186,000 miles per second = c = speed of light ! They move through vacuum,and do not need a ' carrier'. Speed decreases after entering materials.1
Light is a form of electromagnetic radiation. Other forms of electromagnetic radiation include radio waves, microwaves, infrared radiation, ultraviolet rays, X-rays, and gamma rays. All of these, known collectively as the electromagnetic spectrum, are fundamentally similar in that they move at 186,000 miles per second, (299,792 km/sec) the speed of light. The only difference between them is their wavelength, which is directly related to the amount of energy the waves carry. The shorter the wavelength of the radiation, the higher the energy.

The rainbow of colors that we see in visible light represents only a very small portion of the electromagnetic spectrum. On one end of the spectrum are radio waves with wavelengths billions of times longer than those of visible light. On the other end of the spectrum are gamma rays. These have wavelengths millions of times smaller than those of visible light. The following are the basic categories of the electromagnetic spectrum, from longest to shortest wavelength:

Radio waves are used to transmit radio and television signals. Radio waves have wavelengths that range from less than a centimeter to tens or even hundreds of meters. FM radio waves are shorter than AM radio waves. For example, an FM radio station at 100 on the radio dial (100 megahertz) would have a wavelength of about three meters. An AM station at 750 on the dial (750 kilohertz) uses a wavelength of about 400 meters. Radio waves can also be used to create images. Radio waves with wavelengths of a few centimeters can be transmitted from a satellite or airplane antenna. The reflected waves can be used to form an image of the ground in complete darkness or through clouds.

Microwave wavelengths range from approximately one millimeter (the thickness of a pencil lead) to thirty centimeters (about twelve inches). In a microwave oven, the radio waves generated are tuned to frequencies that can be absorbed by the food. The food absorbs the energy and gets warmer. The dish holding the food doesn't absorb a significant amount of energy and stays much cooler. Microwaves are emitted from the Earth, from objects such as cars and planes, and from the atmosphere. These microwaves can be detected to give information, such as the temperature of the object that emitted the microwaves

Infrared is the region of the electromagnetic spectrum that extends from the visible region to about one millimeter (in wavelength). Infrared waves include thermal radiation. For example, burning charcoal may not give off light, but it does emit infrared radiation which is felt as heat. Infrared radiation can be measured using electronic detectors and has applications in medicine and in finding heat leaks from houses. Infrared images obtained by sensors in satellites and airplanes can yield important information on the health of crops and can help us see forest fires even when they are enveloped in an opaque curtain of smoke.

Visible light. The rainbow of colors we know as visible light is the portion of the electromagnetic spectrum with wavelengths between 400 and 700 billionths of a meter (400 to 700 nanometers). It is the part of the electromagnetic spectrum that we see, and coincides with the wavelength of greatest intensity of sunlight. Visible waves have great utility for the remote sensing of vegetation and for the identification of different objects by their visible colors.

Ultraviolet radiation has a range of wavelengths from 400 billionths of a meter to about 10 billionths of a meter. Sunlight contains ultraviolet waves which can burn your skin. Most of these are blocked by ozone in the Earth's upper atmosphere. A small dose of ultraviolet radiation is beneficial to humans, but larger doses cause skin cancer and cataracts. Ultraviolet wavelengths are used extensively in astronomical observatories. Some remote sensing observations of the Earth are also concerned with the measurement of ozone.

X-rays are high energy waves which have great penetrating power and are used extensively in medical applications and in inspecting welds. X-ray images of our Sun can yield important clues to solar flares and other changes on our Sun that can affect space weather. The wavelength range is from about ten billionths of a meter to about 10 trillionths of a meter.

Gamma rays have wavelengths of less than about ten trillionths of a meter. They are more penetrating than X-rays. Gamma rays are generated by radioactive atoms and in nuclear explosions, and are used in many medical applications. Images of our universe taken in gamma rays have yielded important information on the life and death of stars, and other violent processes in the universe.

Cosmic Rays. Despite their name, cosmic rays are not a part of the electromagnetic spectrum. Instead of radiation, cosmic rays are high-energy charged particles that travel through space at nearly the speed of light. Their extremely high energies are comparable to those of gamma rays at the upper end of the electromagnetic spectrum. The highest-energy cosmic rays originate outside our galaxy and provide information on distant objects such as quasars. Cosmic rays are detected when they hit the upper atmosphere, creating showers of particles in their interaction with atoms. These secondary particles can then be detected by instruments on the ground.

The Electromagnetic Waves


ELF WAVES Frequency is 60 Hz, as their sources are any alternating current, especially strong near high voltage transmission lines .
RADIOWAVES AM frequency given by stations: 550 – 1600 kHz (= 1.6 MHz)
FM frequency given by stations: 88 – 108 MHz
AM = amplitude modulated , FM = frequency modulated
TV WAVES TV stations use higher Fr – waves to get better resolution = reception. 54 – 806 MHz , many channels
MICROWAVES CELLULAR PHONE WAVES: frequency – 880 MHz =0.88 GHz , 'cell ' is the area covered by the antenna of( receiving or sending) company - therefore 'hand-off'.
MICROWAVE OVEN – heat water ( in food ) ; 2.45 GHz = 2,450 MHz
RADAR: used ( in conjunction with the Doppler Effect ) in ‘speed traps’ by police, in missiles to find airplanes, tanks, etc.; used by airports to guide airplanes, most 1 – 100 GHz ( G = giga )
INFRARED Just below visible red, also called heat radiation . With special cameras used to find heat losses from houses; by army to detect heat radiation from engines, people.
VISIBLE LIGHT RED, YELLOW, GREEN, BLUE, VIOLET - no white or black !!! White is the sensation for our brain when primary colors ( red, blue and green) fall onto the retina at the same time . Black is the absence of any light .
ULTRAVIOLET ALPHA- UV is energetic enough to cuase chemical reaction BETA UV causes damage to cell structure (tanning) and can cause genetic damage to cell DNA => possible cancer .
X-RAYS SOFT - X rays = lower Fr – range; used for taking x-ray pictures.
HARD - X - rays = higher Fr –range; used in cancer treatments to kill cancer cells.
GAMMA RAYS Frequency range overlaps with hard X-rays. Gamma rays originate though in the nucleus of atoms, not by electron – jumps between energy levels as frequencies higher than infraded do .
COSMIC RAYS Very high frequency, comes from sun, outer space = universe to us.


EM Spectrum and Analytical Spectroscopy


Radiation
Type
Radiation SourceFrequencyRange (Hz)Wavelength RangeType of Transitions
gamma rays  1020 - 1024<10-12 mnuclear
X-rays 1017 - 10201nm - 1 pminner electron
ultravioletdeuterium lamp1015 - 1017400 nm - 1 nmouter electron. Electronic transitions, vibrational fine structure
visibleTungsten lamp4 - 7.5 x 1014 750 nm - 400 nm
near-infraredTungsten, dye laser1 x 1014 - 4 x 10142500 nm - 750 nm (2.5 um - 750 nm)outer electron molecular vibrations. Vibrational transitions, rotational fine structure
infrarednerst glower, globar, Xe,Ar, discharge lamp1013 - 1014250,000 - 2,500 nm (25um - 2.5 um)outer electron, molecular vibrations. Vibrational transitions, rotational fine structure
microwaves 3 x 1011 - 1013250,000 - 1,000,000,000 nm (1 mm - 25 um)molecular rotations,electron spin flips*, Rotational transitions
radio waves <3 x 1011>1 mmnuclear spin flips*
* energy levels split by a magnetic field.


The Bands of the Electromegnetic Spectrum


Band Wavelength Frequency
MF medium frequency   300-3000 kHz
HF high frequency   3-30 MHz
Radio
FM
ShortWave
20 cm - 20 m
2.5-3.5 m
20 cm - 2.5 m
15 MHz - 1.5 GHz
85-120 MHz
120 MHz - 1.5 GHz
Microwave 0.01-20 cm 1.5-3000 GHz
EHF extremely high frequency   30-300 GHz
Far Infrared 20,000-100,000 nm 3000-15000 GHz
Near Infrared 700-20,000 nm 15000-430,000 GHz
Visible
Red
Orange
Yellow
Green
Blue
Violet
400-700 nm
620-760 nm
570-620 nm
550-570 nm
470-550 nm
440-470 nm
380-440 nm
430,000-750,000 GHz
Ultraviolet 50-190-400 nm 1015 - 1017 Hz
Soft XRay 1-20 nm 1017 - 1020 Hz
Hard XRay 0.1-1 nm  
Gamma ray 0.1 - 0.000001 nm Highest 1020 - 1024 Hz


EM Specrtum used in Broadcasting and Wirelass

Some common frequency bands

AM radio535 kilohertz to 1.7 megahertz
Short wave radio5.9 megahertz to 26.1 megahertz
Citizens band (CB) radio26.96 megahertz to 27.41 megahertz
Television stations, channels 2 through 654 to 88megahertz
FM radio88 megahertz to 108 megahertz
Television stations, channels 7 through 13174 to 220 megahertz

Some Wireless Technology Bands

Garage door openers, alarm systemsAround 40 megahertz
Standard cordless phones40 to 50 megahertz
Baby monitors49 megahertz
Radio controlled airplainsAround 72 megahertz
Radio controlled cars (different from above)Around 75 megahertz
Wildlife tracking collars215 to 220 megahertz
MIR space station145 to 437 megahertz
Cell phones824 to 849 megahertz
New 900 MHz cordless phonesAround 900 megahertz (obviously)z
Air traffic control radar960 to 1,215 megahertz
Global Positioning System1,227 and 1,575 megahertz
Deep space radio communications2,290 megahertz to 2,300 megahertz


1. Reference: http://howstuffworks.com
(a) Nature of EM radiation (S.H. Neaves, M. W. Davidson)
(b) The Radio Spectrum (Marshall Brain)


delloyd.50megs.com


Signature: Dhanlal De Lloyd, Chem. Dept, The University of The West Indies, St. Augustine campus
The Republic of Trinidad and Tobago.
Copyright: delloyd2000© All rights reserved.