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EM spectrum and chemistry
Instrument parameters in spectroscopy
Visible and complimentary colors
The Electromagnetic Spectrum of RadiationThe 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
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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 Source FrequencyRange (Hz) Wavelength Range Type of Transitions gamma rays 1020 - 1024 <10-12 m nuclear X-rays 1017 - 1020 1nm - 1 pm inner electron ultraviolet deuterium lamp 1015 - 1017 400 nm - 1 nm outer electron. Electronic transitions, vibrational fine structure visible Tungsten lamp 4 - 7.5 x 1014 750 nm - 400 nm near-infrared Tungsten, dye laser 1 x 1014 - 4 x 1014 2500 nm - 750 nm (2.5 um - 750 nm) outer electron molecular vibrations. Vibrational transitions, rotational fine structure infrared nerst glower, globar, Xe,Ar, discharge lamp 1013 - 1014 250,000 - 2,500 nm (25um - 2.5 um) outer electron, molecular vibrations. Vibrational transitions, rotational fine structure microwaves magnetron 3 x 1011 - 1013 250,000 - 1,000,000,000 nm (1 mm - 25 um) molecular rotations,electron spin flips*, Rotational transitions radio waves <3 x 1011 >1 mm nuclear 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
20 cm - 20 m
20 cm - 2.5 m
15 MHz - 1.5 GHz
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
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 WirelassSome common frequency bands
AM radio 535 kilohertz to 1.7 megahertz Short wave radio 5.9 megahertz to 26.1 megahertz Citizens band (CB) radio 26.96 megahertz to 27.41 megahertz Television stations, channels 2 through 6 54 to 88megahertz FM radio 88 megahertz to 108 megahertz Television stations, channels 7 through 13 174 to 220 megahertz
Some Wireless Technology Bands
Garage door openers, alarm systems Around 40 megahertz Standard cordless phones 40 to 50 megahertz Baby monitors 49 megahertz Radio controlled airplains Around 72 megahertz Radio controlled cars (different from above) Around 75 megahertz Wildlife tracking collars 215 to 220 megahertz MIR space station 145 to 437 megahertz Cell phones 824 to 849 megahertz New 900 MHz cordless phones Around 900 megahertz (obviously)z Air traffic control radar 960 to 1,215 megahertz Global Positioning System 1,227 and 1,575 megahertz Deep space radio communications 2,290 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)