Electromagnetic Spectrum

Comparison of energies on the EMS

Applet ctrum/s.htm This site allows you to move around the EMS to compare the various energies with respect to frequency and wavelength.

Radio Waves A radio wave is an electromagnetic wave propagated by an antenna. Radio waves have different frequencies, and by tuning a radio receiver to a specific frequency you can pick up a specific signal. Radio signals have very long wavelengths. AM radio Short wave CBCB TV 2-6 TV 7-13FM radio

Common frequency bands include the following: AM radio kilohertz to 1.7 megahertz Short wave radio - bands from 5.9 megahertz to 26.1 megahertz Citizens band (CB) radio megahertz to megahertz Television stations - 54 to 88 megahertz for channels 2 through 6 FM radio - 88 megahertz to 108 megahertz Television stations to 220 megahertz for channels 7 through 13

Other devices that use radio energy (each with their own frequency range!) Garage door openers, alarm systems Standard cordless phones Baby monitors Radio controlled air planes Radio controlled cars Wildlife tracking collars MIR space station Cell phones New 900-MHz cordless phones Air traffic control radar Global Positioning System Deep space radio communications Our classroom remote for the computer

Microwaves A microwave oven uses microwaves to heat food. Microwaves are radio waves. In the case of microwave ovens, the commonly used radio wave frequency is roughly 2,500 megahertz (2.5 gigahertz).

Microwaves Radio waves in this frequency range have an interesting property: they are absorbed by water, fats and sugars. When they are absorbed they are converted directly into atomic motion -- heat. Microwaves in this frequency range have another interesting property: they are not absorbed by most plastics, glass or ceramics. Metal reflects microwaves, which is why metal pans do not work well in a microwave oven.

Infrared Energy All of the objects around you are radiating infrared energy right now, even the desks and books! Human beings don't have any sensors that can detect subtle differences in infrared, but our skin can detect objects radiating lots of infrared energy. When you warm yourself by standing close to a fire, the "warmth" is infrared energy that you are absorbing. Some IR arrives from the sun (greenhouse effect).

Objects that make use of IR technology Ear Thermometers Thermal imaging Motion detectors (garage lights) Burglar alarms (motion sensors) Night vision scopes, goggles, cameras Daylight Night, w/o deviceNight, w/device

Visible light occupies only one-thousandth of a percent of the EMS. Anything that produces light does it by energizing atoms in some way. More about color and visible light later.

Items that give off visible light Halogen lamps Gas lanterns Fluorescent lights Lasers Glow-in-the-dark toys Indiglo watches Chemical light sticks - use a chemical reaction to energize atoms. (So do fireflies.)

Ultraviolet light Higher energy than visible light. Arrives on earth from the sun. In small doses, can be beneficial (helps our bodies make Vitamin D). In large doses, can be harmful (sunburn, sun poisoning, skin cancer, cateracts. Most UV light blocked by ozone layer.

Devices the make use of UV Germicidal lamps (like in our goggle cabinet) for air and water disinfection. Black lights (Lamps that give off UV radiation): used to - detect antique forgeries - detect leaks in machinery by repair persons - detect counterfeit money - detect invisible hand stamps for re-admission to events - identify bodily fluids by forensic scientists

X-rays Used in medical diagnostic applications Very high energy — having an x-ray should not be a daily occurrence! (Unless medically necessary) Lead metal used to block transmission (like the lead apron put on you at the dentist ’ s office when having x-rays taken). Discovered by Wilhelm Roentgen in Called “ X ” rays because the cause was unknown (at the time). High energy X-rays used for radiation therapy for cancer patients.

Gamma rays Given off in nuclear reactions Used in many medical applications (some kinds of radiation therapy for cancer patients). Extremely high energy (very limited exposure). Can only be blocked by 3 feet of concrete!