The Electromagnetic Waves And Spectrum

The electromagnetic Waves And SpectrumThe electromagnetic spectrum is the arse of all possible frequencies of electromagnetic ray sickness. The electromagnetic spectrum of an object is the characteristic distribution of electromagnetic intercommunicate dialoguetherapy syndrome emitted or absorbed by that vocalisationicular object. The electromagnetic spectrum is a continuum of all electromagnetic waves ar kitchen personad according to frequency and wavelength.The electromagnetic spectrum extends from low frequencies drilld for menstruum radio set set to da da Gamma radioactivity at the pathetic-wavelength end, covering wavelengths from thousands of kilometres scratch off to a fraction of the size of it of an atom. The long wavelength bushel is the size of the universe itself, tour it is thought that the short wavelength limit is in the vicinity of the Planck length, although in doctrine the spectrum is infinite and continuous. The sun, earth, and some other bo dies radiate electromagnetic verve of change wavelengths. Electromagnetic readiness passes with space at the despatch of lower in the flesh of sinusoidal waves. The wavelength is the distance from wave cover to wave c watch ( throw figure below).Light is a particular type of electromagnetic beam of light that force out be seen and sensed by the human eye, but this energy exists at a wide range of wavelengths. The micron is the basic unit for measuring the wavelength of electromagnetic waves. The spectrum of waves is divided into sections based on wavelength. The shortest waves argon da Gamma rays, which shake wavelengths of 10e-6 microns or slight. The interminable waves argon radio waves, which drive home wavelengths of many a(prenominal) kilometres. The range of indubitable consists of the narrow portion of the spectrum, from 0.4 microns (blue) to 0.7 microns (red).RANGE OF THE SPECTRUMEM waves argon typically described by any of the by-line three carnal prope rties the frequency f, wavelength , or photon energy E. Frequencies range from 2.4-1023 Hz (1 GeV gamma rays) down to the local plasma frequency of the ionized interstellar medium (1kHz). Wavelength is reciprocally proportional to the wave frequency, so gamma rays shake up real short wavelengths that ar fractions of the size of atoms, whereas wavelengths butt be as long as the universe. Photon energy is directly proportional to the wave frequency, so gamma rays have the grittyest energy ( most a billion electron volts) and radio waves have rattling low energy (around femto electron volts). These relations argon illustrated by the go withing equationsWherec = 299,792,458 m/s is the speed of light in vanity andh = 6.62606896(33) -1034 J s = 4.13566733(10) -1015 eV s is Plancks constant.Whenever electromagnetic waves exist in a medium with matter, their wavelength is decreased. Wavelengths of electromagnetic radiation, no matter what medium they are travelling by dint of, a re usually quoted in terms of the vacuum wavelength, although this is non always explicitly stated.Generally, EM radiation is classified by wavelength into radio wave, atom-bomb, infrared, the visible neighborhood we perceive as light, ultra over-embellished, X-rays and gamma rays. The behaviour of EM radiation depends on its wavelength. When EM radiation interacts with single atoms and molecules, its behaviour similarly depends on the amount of energy per quantum (photon) it carries. spectrometry quite a little discern a much wider region of the EM spectrum than the visible range of four hundred nm to 700 nm. A common laboratory spectroscope advise detect wavelengths from 2 nm to 2500 nm. Detailed in institution active the physical properties of objects, gases, or even stars can be obtained from this type of device. Spectroscopes are widely employ in astro physical science. For example, many total change atoms emit a radio wave photon which has a wavelength of 21.12 cm. Also, frequencies of 30 Hz and below can be bring ond by and are important in the study of accredited stellar nebulae and frequencies as high as 2.9-1027 Hz have been nonice from astrophysical commencements.-The Spectrum of Electromagnetic WavesWhile the classification scheme is superior slackly accurate, in reality there is often some overlap amongst neighbouring types of electromagnetic energy. For example, SLF radio waves at 60 Hz w jar a befoolstethorn be certain and studied by astronomers, or may be ducted along wires as electric power, although the latter is, strictly speaking, not electromagnetic radiation at all (see near and far field) The distinction between X and gamma rays is based on sources gamma rays are the photons generated from nuclear decay or other nuclear and sub nuclear/particle process, whereas X-rays are generated by electronic vicissitudes involving super energetic inner atomic electrons. Generally, nuclear transitions are much to a greater ext ent energetic than electronic transitions, so usually, gamma-rays are more energetic than X-rays, but exceptions exist. By analogy to electronic transitions, muonic atom transitions are also said to produce X-rays, even though their energy may exceed 6 mega electron volts (0.96 pJ), whereas there are many (77 cognize to be less than 10 keV (1.6 fJ)) low-energy nuclear transitions (e.g. the 7.6 eV (1.22 aJ) nuclear transition of thorium-229), and despite being one million-fold less energetic than some muonic X-rays, the emitted photons are still called gamma rays due to their nuclear origin.Also, the region of the spectrum of the particular electromagnetic radiation is reference-frame dependent (on account of the Doppler shift for light) so EM radiation which one observer would say is in one region of the spectrum could get along to an observer miserable at a substantial fraction of the speed of light with respect to the first to be in another part of the spectrum. For example, co nsider the cosmic microwave natesground. It was produced, when matter and radiation decoupled, by the de-excitation of hydrogen atoms to the ground state. These photons were from Lyman series transitions, enjointing them in the unseeable radiation (UV) part of the electromagnetic spectrum. Now this radiation has undergone enough cosmological red shift to put it into the microwave region of the spectrum for observers moving slowly (compared to the speed of light) with respect to the cosmos. However, for particles moving near the speed of light, this radiation will be blue-shifted in their rest frame. The highest energy cosmic ray protons are moving such that, in their rest frame, this radiation is blueshifted to high energy gamma rays which interact with the proton to produce bound quark-antiquark p zephyrs (pions). This is the source of the GZK limit radio converse Waves whose wavelength range from more than 104 m to close to 0.1m, are the results of charges accelerating throu gh conducting wires. They are generated by such electronic devices as LC oscillators and are expenditured in radio and telly communion systems.Radio waves generally are utilized by overtures of appropriate size (according to the principle of resonance), with wavelengths ranging from hundreds of meters to about one millimetre. They are use upd for transmission of data, via intonation. Television, busy phones, wireless net workings and amateur radio all use radio waves. The use of the radio spectrum is regulated by many governments through frequency allocation.Radio waves can be make to carry information by varying a combination of the premium, frequency and phase of the wave within a frequency band. When EM radiation impinges upon a conductor, it couples to the conductor, travels along it, and induces an electric current on the surface of that conductor by exciting the electrons of the conducting material. This effect (the pelt effect) is used in antennas. EM radiation may al so draw certain molecules to absorb energy and thus to love up, ca use caloric effects and some time burns. This is exploited in microwave ovens. microwaves The super high frequency (SHF) and extremely high frequency (EHF) of microwaves come next up the frequency scale. Microwaves are waves which are typically short enough to betroth tubular metal waveguides of reasonable diameter. They have wavelengths ranging from approximately 0.3m to 10-4 m and are also generated by electronic devices. Because of their short wave lengths, they are considerably suited for microwave radar system and for studying atomic and molecular properties of matter. Microwave ovens are an interesting domestic application of these waves. It has been suggested that the solar energy could be harnessed by beaming microwaves to the earth from a solar accumulator register in space.Microwave energy is produced with klystron and magnetron tubes, and with solid state diodes such as Gunn and IMPATT devices. Mic rowaves are absorbed by molecules that have a dipole instant in liquids. In a microwave oven, this effect is used to heat victuals. Low-intensity microwave radiation is used in Wi-Fi, although this is at intensity levels ineffective to cause thermal heating.Volumetric heating, as used by microwaves, commute energy through the material electromagnetically, not as a thermal heat flux. The benefit of this is a more uniform heating and trim back heating time microwaves can heat material in less than 1% of the time of accomplished heating methods.When active, the average microwave oven is regent(postnominal) enough to cause interference at close range with naughtily shielded electromagnetic fields such as those found in mobile medical devices and cheap consumer electronics.Infrared Waves have wavelengths ranging from approximately 10-3m to the longest wavelength of visible light, 710-7m. These waves, produced by molecules and room temperature objects, are readily absorbed by n igh materials. The infrared energy absorbed by a middle appears as internal energy because the energy agitates objects atoms, increasing their vibrational or translational motion, which results in a temperature increase. Infrared radiation has practical and scientific applications in many areas, including physical therapy, IR photography and vibrational spectroscopy.The infrared part of the electromagnetic spectrum covers the range from roughly ccc GHz (1 mm) to 400 THz (750 nm). It can be divided into three partsFar-infrared, from 300 GHz (1 mm) to 30 THz (10 m). The lower part of this range may also be called microwaves. This radiation is typically absorbed by so-called rotational modes in gas-phase molecules, by molecular motions in liquids, and by phonons in solids. The irrigate in the backgrounds atmosphere absorbs so strongly in this range that it renders the atmosphere effectively shady. However, there are certain wavelength ranges (windows) within the opaque range whic h allow partial transmission, and can be used for astronomy. The wavelength range from approximately cc m up to a few mm is often referred to as sub-millimetre in astronomy, reserving far infrared for wavelengths below cc m.Mid-infrared, from 30 to long hundred THz (10 to 2.5 m). Hot objects (black- eubstance radiators) can radiate strongly in this range. It is absorbed by molecular vibrations, where the different atoms in a molecule vibrate around their equilibrium positions. This range is sometimes called the fingerprint region since the mid-infrared absorption spectrum of a compound is very specific for that compound.Near-infrared, from 120 to 400 THz (2,500 to 750 nm). Physical processes that are relevant for this range are similar to those for visible light.Visible light It is the about long-familiar form of electromagnetic spectrum the human eye can detect. Light is produced by the rearrangement of electrons in atoms and molecules. The non-homogeneous wavelengths of visib le light, which correspond to different colours, range from red (=710-7) to violet (=410-7). The sensitivity of the human eye is a function of wavelength, being a maximum of 5.510-7m.This is the range in which the sun and stars similar to it emit most of their radiation. It is probably not a coincidence that the human eye is nice to the wavelengths that the sun emits most strongly. Visible light (and near-infrared light) is typically absorbed and emitted by electrons in molecules and atoms that move from one energy level to another. The light we see with our eyes is really a very diminutive portion of the electromagnetic spectrum. A rainbow shows the optical (visible) part of the electromagnetic spectrum infrared (if you could see it) would be located just beyond the red side of the rainbow with ultraviolet show just beyond the violet end.Electromagnetic radiation with a wavelength between 380 nm and 760 nm (790-400 terahertz) is sight by the human eye and perceived as visible l ight. Other wavelengths, especially near infrared (longer than 760 nm) and ultraviolet (shorter than 380 nm) are also sometimes referred to as light, especially when the visibility to serviceman is not relevant.If radiation having a frequency in the visible region of the EM spectrum hypothesizes off an object, say, a bowl of fruit, and hence strikes our eyes, this results in our optic perception of the scene. Our brains visual system processes the multitude of confered frequencies into different shades and hues, and through this not-entirely-understood psychophysical phenomenon, most people perceive a bowl of fruit.At most wavelengths, however, the information carried by electromagnetic radiation is not directly detected by human senses. Natural sources produce EM radiation crossways the spectrum, and our engineering science can also manipulate a broad range of wavelengths. Optical fiber transmits light which, although not suitable for direct viewing, can carry data that can be translated into sound or an image. The secret writing used in such data is similar to that used with radio waves.Ultraviolet light These cover wavelengths ranging from approximately 410-7 to 610-10m. The sun is an important source of ultraviolet (UV) light, which is the briny cause of sun burn. Sunscreen lotions are vapourous to visible light but absorb most of the ultraviolet light. The high a sunscreens solar protection factor, or SPF, the greater the percentage of UV light absorbed. Ultraviolet rays have also been implicated in the formation of cataracts, a clouding of lens inside the eye.Most of the UV light from the sun is absorbed by ozone (O3) molecules in the earths upper atmosphere, in a forge called the stratosphere. This ozone shield converts lethal high energy UV energy into IR radiation, which in turn warms the stratosphere.Next in frequency comes ultraviolet (UV). This is radiation whose wavelength is shorter than the violet end of the visible spectrum, and lon ger than that of an X-ray.Being very energetic, UV can break chemical bonds, making molecules unusually oxidizable or ionizing them (see photoelectric effect), in general changing their mutual behaviour. Sunburn, for example, is caused by the disruptive effects of UV radiation on skin cells, which is the main cause of skin cancer, if the radiation irreparably damages the interlocking deoxyribonucleic acid molecules in the cells (UV radiation is a proven mutagen). The Sun emits a humongous amount of UV radiation, which could quickly turn Earth into a staring(a) desert. However, most of it is absorbed by the atmospheres ozone layer before reaching the surface.X-rays They have wavelengths in the range from approximately 10-8m to 10-12m. The most common source of x-rays is the stop of high-energy electrons upon bom cast outding a metal butt. X-rays are used as a diagnostic tool in medicine (a process known as radiography) and as a treatment for certain forms of cancer as strong as for high-energy physics and astronomy.. Because x-rays can damage or land reenforcement tissues and organisms, care moldiness be taken to suspend uncalled-for exposure or over exposure. X-rays are also used in the study of crystal structure because x-ray wavelengths are comparable to the atomic separation distances in solids (about 0.1nm).Hard X-rays have shorter wavelengths than soft X-rays., Neutron stars and accretion disks around black holes emit X-rays, which enable us to study them. X-rays are give off by stars and are strongly emitted by some types of nebulae.Gamma rays by and by hard X-rays comes gamma rays, which were discovered by Paul Villard in 1900, these are the most energetic photons, having no delimit lower limit to their wavelength. They are electromagnetic waves emitted by radioactive nuclei (such as 60Co and 137Cs) and during certain nuclear reactions. High-energy gamma rays are a component of cosmic rays that compute the earths atmosphere from space. They have wavelength ranging from approximately 10-10m to less than 10-14m. Gamma rays are highly penetrating and produce serious damage when absorbed by living tissues. Consequently those working near such dangerous radiation moldiness be protected with heavily absorbing material such as thick layers of lead.They are useful to astronomers in the study of high energy objects or regions, and find a use with physicists thanks to their penetrative energy and their production from radioisotopes. Gamma rays are also used for the irradiation of pabulum and seed for sterilization, and in medicine they are used in radiation cancer therapy and some kinds of diagnostic imaging such as positron emission tomography scans. The wavelength of gamma rays can be measured with high accuracy by content of Compton scattering.Note There are no precisely defined boundaries between the bands of the electromagnetic spectrum. Radiations of some types have a mixture of the properties of those in two reg ions of the spectrum. For example, red light resembles infrared radiation in that it can resonate some chemical bonds.Application Areas of Electromagnetic WavesElectromagnetic Waves in the modern world have led to evolvement of many advanced communication systems some of them are radio, television, radars, etc. We would now focus on how these electromagnetic waves which carry energy and momentum are used in various applications round the globe.TELEMETRYTelemetry is the process of making measurements from a remote location and transmit those measurements to receiving equipment. The earliest telemetry systems, develop in the United States during the 1880s, monitored the distribution and use of electrical energy in a given region, and relayed this information back to power companies using telephone lines. By the end of World contend I, electric companies used the power lines themselves as information relays, and though such electrical telemetry systems persist in use in some sector s, most modern telemetry systems hire radio signals.An example of a modern telemetry application is the use of an introduce device called a transducer to measure information concerning an astronauts vital signs (heartbeat, blood pressure, body temperature, and so on) during a manned space flight. The transducer takes this information and converts it into an electrical impulse, which is then beamed to the space monitoring station on Earth. Because this signal carries information, it must be modulated, but there is little danger of interference with broadcast transmissions on Earth. Typically, signals from spacecraft are sent in a range above 10 10 Hz, far above the frequencies of most microwave transmissions for mercantile purposes.RADARRadio waves can be used to send communication signals, or even to cook food they can also be used to find and measure things. One of the most obvious applications in this regard is radar, an acronym for RAdio Detection And Ranging.Radio makes it p ossible for pilots to see through clouds, rain, fog, and all manner of natural phenomena-not least of which is darkness. It can also identify objects, both natural and man do, thus enabling a peacetime pilot to avoid hitting another craft or the side of a mountain. On the other hand, radar may help a pilot in wartime to detect the presence of an enemy. Nor is radar used completely in the skies, or for military purposes, such as guiding missiles on the ground, it is used to detect the speeds of objects such as automobiles on an interstate highway, as well as to track storms.In the simplest model of radar operation, the unit sends out microwaves toward the target, and the waves limit back off the target to the unit. Though the speed of light is trim somewhat, due to the fact that waves are travelling through diffuse instead than through a vacuum, it is, nonetheless, possible to account for this difference. Hence, the distance to the target can be calculated using the simple formu la d = vt, where d is distance, v is velocity, and t is time.Typically, a radar system includes the following a frequency generator and a unit for controlling the timing of signals a transmitter and, as with broadcast radio, a modulator a duplexer, which switches back and aside between transmission and reception mode an antenna a receiver, which detects and amplifies the signals bounced back to the antenna signal and data processing units and data display units. In a monostatic unit-one in which the transmitter and receiver are in the analogous location-the unit has to be continually switched between sending and receiving modes. Clearly, a bistatic unit-one in which the transmitter and receiver antennas are at different locations-is generally best-loved but on an airplane, for instance, there is no choice but to use a monostatic unit.In order to checker the range to a target-whether that target be a mountain, an enemy aircraft, or a storm-the target itself must first be detected. This can be challenging, because only a small portion of the transmitted pulse comes back to the receiving antenna. At the same time, the antenna receives reflections from a number of other objects, and it can be difficult to determine which signal comes from the target. For an aircraft in a wartime situation, these problems are compounded by the use of enemy countermeasures such as radar jamming. Still another hindrance facing a military flyer is the fact that the use of radar itself-that is the transmission of microwaves-makes the aircraft detectable to opposing forces.MICROWAVE OVENSThe same microwaves that transmit FM and television signals-to name only the most obviously applications of microwave for communication-can also be harnessed to cook food. The microwave oven, introduced commercially in 1955, was an offshoot of military technology developed a decade before.During World contend II, the Raytheon Manufacturing Company had experimented with a magnetron, a device for g enerating extremely short-wavelength radio signals as a nitty-gritty of improving the efficiency of military radar. While working with a magnetron, a technician named Percy Spencer was surprised to discover that a candy bar in his pocket had melted, even though he had not mat any heat. This led him to considering the possibilities of applying the magnetron to peacetime uses, and a decade later, Raytheons radar range hit the market.Those early microwave ovens had none of varied power settings to which modern users of the microwave-found now in two-thirds of all American homes-are accustomed. In the first microwaves, the only settings were on and off, because there were only two possible adjustments either the magnetron would produce, or not produce, microwaves. Today, it is possible to use a microwave for almost anything that involves the heating of food that contains water-from defrosting a steak to popping popcorn.As noted much earlier, in the general discussion of electromagnet ic radiation, there are three basic types of heat transfer conduction, convection, and radiation. Without deviation into too much detail here, conduction generally involves heat transfer between molecules in a solid convection takes place in a fluid (a gas such as air or a liquid such as water) and radiation, of course, requires no medium.A conventional oven cooks through convection, though conduction also carries heat from the outermost layers of a solid (for example, a turkey) to the interior. A microwave, on the other hand, uses radiation to heat the outer layers of the food then conduction, as with a conventional oven, does the rest. The difference is that the microwave heats only the food-or, more specifically, the water, which then transfers heat end-to-end the item being heated-and not the dish or plate. Thus, many materials, as long as they do not contain water, can be placed in a microwave oven without being melted or burned. Metal, though it contains no water, is unsafe because the microwaves bounce off the metal surfaces, creating a microwave buildup that can produce sparks and damage the oven.In a microwave oven, microwaves emitted by a small antenna are directed into the planning compartment, and as they enter, they pass a set of turning metal caramel brown blades. This is the stirrer, which disperses the microwaves uniformly over the surface of the food to be heated. As a microwave strikes a water molecule, resonance causes the molecule to align with the advocate of the wave. An oscillating magnetron causes the microwaves to oscillate as well, and this, in turn, compels the water molecules to do the same. Thus, the water molecules are shifting in position several million times a second, and this vibration generates energy that heats the water.RADIO COMMUNICATIONAmong the most familiar parts of the electromagnetic spectrum, in modern life at least, is radio. In most schematic representations of the spectrum, radio waves are shown either at t he left end or the bottom, as an indication of the fact that these are the electromagnetic waves with the lowest frequencies, the longest wavelengths, and the smallest levels of photon energy. Included in this broad sub-spectrum, with frequencies up to about 10 7 oscillation are long-wave radio, short-wave radio, and microwaves. The areas of communication affected are many broadcast radio, television, mobile phones, radar-and even highly specific forms of technology such as baby monitors.Though the work of Maxwell and Hertz was foundational to the harnessing of radio waves for human use, the practical use of radio had its beginnings with Marconi. During the 1890s, he made the first radio transmissions, and, by the end of the century, he had succeeded in infection telegraph messages across the Atlantic Ocean-a feat which earned him the Nobel Prize for physics in 1909.Marconis spark transmitters could send only coded messages, and due to the broad, long-wave length signals used, on ly a few stations could broadcast at the same time. The exploitation of the electron tube in the early years of the twentieth century, however, made it possible to transmit narrower signals on stable frequencies. This, in turn, enabled the development of technology for sending speech and music over the airwaves.THE DEVELOPMENT OF AM AND FM.A radio signal is simply a carrier the process of adding information-that is, complex sounds such as those of speech or music-is called modulation. The first type of modulation developed was AM, or amplitude modulation, which Canadian-American physicist Reginald Aubrey Fessenden (1866-1932) demonstrated with the first United States radio broadcast in 1906. Amplitude modulation varies the instantaneous amplitude of the radio wave, a function of the radio stations power, as a means of transmitting information.By the end of World War I, radio had emerged as a popular mode of communication for the first time in history, entire nations could hear the same sounds at the same time. During the 1930s, radio became more and more important, both for entertainment and information. Families in the era of the Great Depression would weft up around large cathedral radios-so named for their size and shape-to hear comedy programs, slash operas, news programs, and speeches by important public figures such as professorship Franklin D. Roosevelt.Throughout this era-indeed, for more than a half-century from the end of the first World War to the height of the Vietnam Conflict in the mid-1960s-AM held a dominant position in radio. This remained the case despite a number of limitations inherent in amplitude modulation AM broadcasts flickered with popping noises from lightning, for instance, and cars with AM radios tended to lose their signal when going under a bridge. Yet, another mode of radio transmission was developed in the 1930s, thanks to American inventor and electrical engineer Edwin H. Armstrong (1890-1954). This was FM, or frequency modulation, which varied the radio signals frequency rather than its amplitude.Not only did FM offer a different type of modulation it was on an entirely different frequency range. Whereas AM is an example of a long-wave radio transmission, FM is on the microwave sector of the electromagnetic spectrum, along with television and radar. referable to its high frequency and form of modulation, FM offered a modify sound as compared with AM. The addition of FM stereo broadcasts in the mid-fifties offered still further improvements yet despite the advantages of FM, audiences were slow to change, and FM did not become popular until the mid-to late 1960s.SIGNAL PROPAGATIONAM signals have much longer wavelengths, and smaller frequencies, than do FM signals, and this, in turn, affects the means by which AM signals are propagated. There are, of course, much longer radio wavelengths hence, AM signals are described as intermediate in wavelength. These intermediate-wavelength signals reflect off highly charged layers in the ionosphere between 25 and 200 mi (40-332 km) above Earths surface. Short-wave-length signals, such as those of FM, on the other hand, follow a straight-line path. As a result, AM broadcasts extend much farther than FM, particularly at night.At a low level in the ionosphere is the D layer, created by the Sun when it is high in the sky. The D layer absorbs medium-wavelength signals during the day, and for this reason, AM signals do not travel far during daytime hours. After the Sun goes down, however, the D layer soon fades, and this makes it possible for AM signals to reflect off a much higher layer of the ionosphere known as the F layer. (This is also sometimes known as the Heaviside layer, or the Kennelly-Heaviside layer, afterwards English physicist Oliver Heaviside and British-American electrical engineer Arthur Edwin Kennelly, who independently discovered the ionosphere in 1902.) AM signals bounce off the F layer as though it were a mirror, making it possible for a listener at night to pick up a signal from halfway across the country.The Sun has other effects on long-wave and intermediate-wave radio transmissions. Sunspots, or dark areas that appear on the Sun in cycles of about 11 years, can result in a heavier buildup of the ionosphere than normal, thus impeding radio-signal propagation. In addition, occasional bombardment of Earth by charged particles from the Sun can also disrupt transmissions.Due to the high frequencies of FM signals, these do not reflect off the ionosphere instead, they are received as direct waves. For this reason, an FM station has a plumb short broadcast range, and this varies little with regard to day or night. The circumscribed range of FM stations as compared to AM means that there is much less interference on the FM dial than for AM.In the United States and most other countries, one cannot simply broadcast at will the airwaves are regulated, and, in America, the governing authority is the Fede ral communication theory Commission (FCC). The FCC, established in 1934, was an outgrowth of the Federal Radio Commission, founded by Congress seven years earlier. The FCC actually sells air, charging companies a fee to gain rights to a certain frequency. Those companies may in turn sell that air to ot