The short answer is that scientists don't like to use numbers any bigger or smaller than they have to. It is much easier to say or write "two kilometers" than "two thousand meters.
Astronomers who study radio waves tend to use wavelengths or frequencies. Most of the radio part of the EM spectrum falls in the range from about 1 cm to 1 km, which is 30 gigahertz GHz to kilohertz kHz in frequencies.
The radio is a very broad part of the EM spectrum. Infrared and optical astronomers generally use wavelength. Infrared astronomers use microns millionths of a meter for wavelengths, so their part of the EM spectrum falls in the range of 1 to microns. Optical astronomers use both angstroms 0. Using nanometers, violet, blue, green, yellow, orange, and red light have wavelengths between and nanometers.
This range is just a tiny part of the entire EM spectrum, so the light our eyes can see is just a little fraction of all the EM radiation around us. The wavelengths of ultraviolet, X-ray, and gamma-ray regions of the EM spectrum are very small. Instead of using wavelengths, astronomers that study these portions of the EM spectrum usually refer to these photons by their energies, measured in electron volts eV.
Ultraviolet radiation falls in the range from a few electron volts to about eV. X-ray photons have energies in the range eV to , eV or keV. Gamma-rays then are all the photons with energies greater than keV. Gamma rays are ionizing radiation and are thus biologically hazardous. They are classically produced by the decay from high energy states of atomic nuclei, a process called gamma decay, but are also created by other processes.
Paul Villard, a French chemist and physicist, discovered gamma radiation in , while studying radiation emitted from radium during its gamma decay. Natural sources of gamma rays on Earth include gamma decay from naturally occurring radioisotopes such as potassium, and also as a secondary radiation from various atmospheric interactions with cosmic ray particles.
Some rare terrestrial natural sources that produce gamma rays that are not of a nuclear origin, are lightning strikes and terrestrial gamma-ray flashes, which produce high energy emissions from natural high-energy voltages.
Gamma rays are produced by a number of astronomical processes in which very high-energy electrons are produced. Such electrons produce secondary gamma rays by the mechanisms of bremsstrahlung, inverse Compton scattering and synchrotron radiation.
Notable artificial sources of gamma rays include fission such as occurs in nuclear reactors, and high energy physics experiments, such as neutral pion decay and nuclear fusion. Gamma rays have characteristics identical to X-rays of the same frequency—they differ only in source. They have many of the same uses as X-rays, including cancer therapy.
Gamma radiation from radioactive materials is used in nuclear medicine. The distinction between X-rays and gamma rays has changed in recent decades. Originally, the electromagnetic radiation emitted by X-ray tubes almost invariably had a longer wavelength than the radiation gamma rays emitted by radioactive nuclei.
However, with artificial sources now able to duplicate any electromagnetic radiation that originates in the nucleus, as well as far higher energies, the wavelengths characteristic of radioactive gamma ray sources vs.
Thus, gamma rays are now usually distinguished by their origin: X-rays are emitted by definition by electrons outside the nucleus, while gamma rays are emitted by the nucleus. Exceptions to this convention occur in astronomy, where gamma decay is seen in the afterglow of certain supernovas, but other high energy processes known to involve other than radioactive decay are still classed as sources of gamma radiation.
A notable example is extremely powerful bursts of high-energy radiation normally referred to as long duration gamma-ray bursts, which produce gamma rays by a mechanism not compatible with radioactive decay.
These bursts of gamma rays, thought to be due to the collapse of stars called hypernovas, are the most powerful events so far discovered in the cosmos. Bright spots within the galactic plane are pulsars spinning neutron stars with strong magnetic fields , while those above and below the plane are thought to be quasars galaxies with supermassive black holes actively accreting matter.
All ionizing radiation causes similar damage at a cellular level, but because rays of alpha particles and beta particles are relatively non-penetrating, external exposure to them causes only localized damage e. Gamma rays and neutrons are more penetrating, causing diffuse damage throughout the body e.
The most biological damaging forms of gamma radiation occur at energies between 3 and 10 MeV. Privacy Policy. Skip to main content. Electromagnetic Waves. Search for:. The Electromagnetic Spectrum. There is a wide range of subcategories contained within radio including AM and FM radio. Radio waves can be generated by natural sources such as lightning or astronomical phenomena; or by artificial sources such as broadcast radio towers, cell phones, satellites and radar. AM waves have constant frequency, but a varying amplitude.
FM radio waves are also used for commercial radio transmission in the frequency range of 88 to MHz. FM stands for frequency modulation, which produces a wave of constant amplitude but varying frequency. Information is carried by amplitude variation, while the frequency remains constant. FM radio waves : Waves used to carry commercial radio signals between 88 and MHz. Information is carried by frequency modulation, while the signal amplitude remains constant.
Microwaves Microwaves are electromagnetic waves with wavelengths ranging from one meter to one millimeter frequencies between MHz and GHz. Learning Objectives Distinguish three ranges of the microwave portion of the electromagnetic spectrum. Key Takeaways Key Points The microwave region of the electromagnetic EM spectrum is generally considered to overlap with the highest frequency shortest wavelength radio waves.
The microwave portion of the electromagnetic spectrum can be subdivided into three ranges listed below from high to low frequencies: extremely high frequency 30 to GHz , super high frequency 3 to 30 GHz , and ultra-high frequency MHz to 3 GHz. Microwave sources include artificial devices such as circuits, transmission towers, radar, masers, and microwave ovens, as well as natural sources such as the Sun and the Cosmic Microwave Background.
Microwaves can also be produced by atoms and molecules. They are, for example, a component of electromagnetic radiation generated by thermal agitation. Key Terms terahertz radiation : Electromagnetic waves with frequencies around one terahertz. Learning Objectives Distinguish three ranges of the infrared portion of the spectrum, and describe processes of absorption and emission of infrared light by molecules.
Key Takeaways Key Points Infrared light includes most of the thermal radiation emitted by objects near room temperature. This is termed thermography, mainly used in military and industrial applications. Key Terms emissivity : The energy-emitting propensity of a surface, usually measured at a specific wavelength. Visible Light Visible light is the portion of the electromagnetic spectrum that is visible to the human eye, ranging from roughly to nm.
Learning Objectives Distinguish six ranges of the visible spectrum. Key Takeaways Key Points Visible light is produced by vibrations and rotations of atoms and molecules, as well as by electronic transitions within atoms and molecules. This figure shows the visible part of the spectrum, together with the colors associated with particular pure wavelengths. Colors that can be produced by visible light of a narrow band of wavelengths are called pure spectral colors.
They can be delineated roughly in wavelength as: violet nm , blue nm , green nm , yellow nm , orange nm , and red to nm. Key Terms spectral color : a color that is evoked by a single wavelength of light in the visible spectrum, or by a relatively narrow band of wavelengths. Every wavelength of light is perceived as a spectral color, in a continuous spectrum; the colors of sufficiently close wavelengths are indistinguishable. The window runs from around nanometers ultraviolet-C at the short end up into the range the eye can use, roughly nm and continues up through the visual infrared to around nm, which is thermal infrared.
Ultraviolet Light Ultraviolet UV light is electromagnetic radiation with a wavelength shorter than that of visible light in the range 10 nm to nm. Learning Objectives Identify wavelength range characteristic for ultraviolet light and its biological effects. Key Takeaways Key Points Ultraviolet light gets its name because the spectrum consists of electromagnetic waves with frequencies higher than those that humans identify as the color violet.
Most UV is non- ionizing radiation, though UV with higher energies nm is ionizing. The Bell Lab scientists soon realized that they had serendipitously discovered the cosmic microwave background radiation. This radiation, which fills the entire universe, is a clue to its beginning, known as the Big Bang. This light, emitted Top of Page Next: Infrared Waves. Retrieved [insert date - e. Science Mission Directorate.
National Aeronautics and Space Administration. This Doppler-radar image seen on TV weather news uses microwaves for local weather forecasting. Shown here is Hurricane Claudette's eye-wall making landfall. Credit: NOAA. This image shows sea ice breaking off the shores of Alaska.
This is an image of the Amazon River in Brazil. It also used awavelengthin the L-band of the microwave spectrum. At one time there was concern that radiation leakage from microwave ovens could interfere with certain electronic cardiac pacemakers. Similar concerns were raised about pacemaker interference from electric shavers, auto ignition systems, and other electronic products.
However, patients with pacemakers are encouraged to consult their physicians if they have concerns. There is little cause for concern about excess microwaves leaking from ovens unless the door hinges, latch, or seals are damaged. The FDA also monitors appliances for radiation safety issues and has received reports of microwave ovens that appear to stay on — and operate — while the door is open.
When operating as intended, microwave ovens have safety features to prevent them from continuing to generate microwaves if the door is open. However, if an oven does continue to operate with the door open, consumers cannot be percent sure that microwave radiation is not being emitted. Thus, if this occurs, the FDA recommends immediately discontinuing use of the oven.
If you suspect a radiation safety problem with your microwave oven, you may contact the microwave oven manufacturer. Manufacturers who discover that any microwave ovens produced, assembled, or imported by them have a defect or fail to comply with an applicable Federal standard are required to immediately notify FDA. You may also report any suspected radiation-related problems or injuries to the FDA by completing and mailing the Accidental Radiation Occurrence Report form.
What is Microwave Radiation? Cooking with Microwaves Microwaves are produced inside the oven by an electron tube called a magnetron. Avoiding Injuries from Super-Heated Water in Microwave Ovens The FDA received reports in the past of serious skin burns or scalding injuries around people's hands and faces as a result of hot water erupting out of a cup after it had been overheated in a microwave oven.
Microwave Ovens and Health Microwave radiation can heat body tissue the same way it heats food. Microwave Ovens and Pacemakers At one time there was concern that radiation leakage from microwave ovens could interfere with certain electronic cardiac pacemakers.
Checking Ovens for Leakage and Other Radiation Safety Problems There is little cause for concern about excess microwaves leaking from ovens unless the door hinges, latch, or seals are damaged. How to Report Microwave Oven Radiation Safety Problems If you suspect a radiation safety problem with your microwave oven, you may contact the microwave oven manufacturer.
Tips on Safe Microwave Oven Operation Follow the manufacturer's instruction manual for recommended operating procedures and safety precautions for your oven model. Use microwave safe cookware specially manufactured for use in the microwave oven. Don't operate a microwave oven if the door does not close firmly or is bent, warped, or otherwise damaged.
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