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1、Sources of EMR Sources of EMR Human Brain Power Lines (50,60Hz) Induction Heating Cell phone Mi- crowave oven Radar Incan- descent light bulb People Radio tower Xray machines Radioac- tive elements Sizes of EMR Sizes of EMR Earth 12,756 km Football Field 100m House 12m Football 308mm People 1.8m Hon
2、ey Bee 1.2cm Single Cell 10m Water Molecule 0.3nm Bacteria 3m- 800nm Virus 17- 300nm GAMMA RAYS X-RAYS ULTRAVIOLET VISIBLE INFRARED MICROWAVERADIO WAVES FrequencyWavelengthEnergy 0.1Hz (Delta brain waves) 3Hz (Theta brain waves)8Hz 8Hz (Alpha brain waves)12Hz (Low Beta brain waves)15Hz (Mid Beta bra
3、in waves)18Hz (High Beta brain waves)30Hz (Gamma brain waves) S S SS SSS 50Hz Power v= 100Hz Lights p= 60Hz Power v= 120Hz Lights p= 400Hz Airplane Power AM Radio 5406007008009001000 110012001300140015001600 C Ground Wave Emergency Network Europe and Asia AM EU where m is the initial electron energy
4、 level and n is the fi nal electron energy level: = 364.56nm m2 m2 n2 Much of the interstellar matter is made of the simplest atom hydrogen. The hydrogen visible-spectrum emission and absorption lines are shown below: HHHHH H H H Emission line Absorption line Balmer series name Power Frequency White
5、 Hot Red Hot Hot CMB Max Planck determined the relationship between the temperature of an object and its radiation pro- fi le; where Ris the radiation power, is the wavelength, T is the temperature: R= 37418 5 14388 T 1 Television Television is transmitted in the VHF and UHF ranges (30MHz - 3GHz). T
6、V channels transmitted over the air are shown as TV . TV channels transmitted through cable (CATV) are shown as TV . CATV channels starting with “T-” are channels fed back to the cable TV station (like news feeds). Air and cable TV stations are broadcast with the separate video, colour, and audio fr
7、equency carriers grouped together in a channel band as follows: 6MHz 1.25MHz 3.58MHz 4.5MHz VideoColourAudio Satellite channels broadcast in the C-Band are depicted as TV . These stations are broadcast in alternating polarities (Ex. Ch 1 is vertical and 2 is horizontal and visa versa on neighbouring
8、 satellites). The 15.7 kHz horizontal sweep signal produced by a TV can be heard by some young people. This common contaminant signal to VLF spectra listening is depicted as . Radio Bands The radio spectrum (ELF to EHF) is populated by many more items than can be shown on this chart, only a small sa
9、mpling of bands used around the world have been shown. Communication using EMR is done using either: Amplitude Modulation (AM) OR Frequency Modulation (FM) Each country has its own rules and regulations for allotting bands in this region. For more information, look up the radio communications author
10、ity in your area (Ex. FCC in the US, DOC in Canada). Not all references agree on the ULF band range, the HAARP range is used here. RAdio Detecting And Ranging (RADAR) uses EMR in the microwave range to detect the distance and speed of objects. Citizens Band Radio (CB) contains 40 stations between 26
11、.965-27.405MHz. Schumann resonance is produced in the cavity between the Earth and the ionosphere. The resonant peaks are depicted asS Hydrogen gas emits radio band EMR at 21cmH Some individual frequencies are represented as icons: xxHzSubmarine communications Time and frequency standards xxm Ham ra
12、dio and international meter bands Miscellaneous short wave radio WWeather stations CPCellular and PCS Phones (including; FDMA, TDMA, CDMA ranges) Sound Although sound waves are not electromagnetic they are included on this chart as a reference in frequency only. All other properties of electromagnet
13、ic waves are diff erent from sound waves. Sound waves are caused by an oscillating compression of molecules. Sound cannot travel in a vacuum such as outer space. The speed of sound in air is 1240kph (770mph). Humans can only hear sound between 20Hz to 20kHz. Infrasound (below 20Hz) can be sensed by
14、internal organs and touch. Frequencies in the 0.2Hz range are often the cause of motion sickness. Bats can hear sound up to 50kHz. The 88 piano keys of the Equal Temperament scale are accurately located on the frequency chart. Over the ages people have striven to divide the continuous audio fre- que
15、ncy spectrum into individual musical notes that have harmonious relationships. Microtonal musicians study various scales. One recent count lists 4700 diff erent musical scales. Middle C is depicted on the chart asC Speaker Ear This image depicts air being compressed as sound waves in a tube fromaspe
16、akerand then travelling through the tube towards the ear. Gravity Waves Gravity is the mysterious force that holds large objects together and binds our planets, stars and galaxies together. Many people have un- successfully theorized about the details of gravity and its relationship to other forces.
17、 There have been no links between gravity waves and electromagnetic radiation. Gravity is theorized to warp space and time. In fact, gravity is re- sponsible for bending light as observed by the gravity-lens example of distant galaxies. “Gravity waves” would appear as ripples in space-time formed by
18、 large objects moving through space that might possibly be detected in the future by very sensitive instruments. The speed that gravity propagates through space has been theorized to be the same as the speed of light. Brain Waves By connecting electrodes from the human head to an electroen- cephalog
19、raph (EEG), it is possible to measure very small cyclic elec- trical signals. There has been much study on this topic, but like all eff ects on humans, the science is not as exact as the science of materials. Generally, lower brain wave frequencies relate to sleep, and the higher frequencies relate
20、to alertness. Devices have been made for measuring and stimulating brain waves to achieve a desired state. Electromagnetic Radiation (EMR) EMR is emitted in discrete units called photons but has properties of waves as seen by the images below. EMR can be created by the oscillation or acceleration of
21、 electrical charge or magnetic fi eld. EMR travels through space at the speed of light (2.997 924 58 108m/s). EMR consists of an oscillating electrical and magnetic fi eld which are at right angles to eachother and spaced at a particular wavelength. There is some controversy about the phase relation
22、ship between the electrical and magnetic fi elds of EMR, one of the theoretical repre- sentations is shown here: +E -E+B -B Source Space E = Electric Field Strength B = Magnetic Field Strength Wave Nature Source Space Particle Nature The particle nature of EMR is exhibited when a solar cell emits in
23、di- vidual electrons when struck with very dim light. The wave nature of EMR is demonstrated by the famous double slit experiment that shows cancelling and addition of waves. Much of the EMR properties are based on theories since we can only see the eff ects of EMR and not the actual photon or wave
24、itself. Albert Einstein theorized that the speed of light is the fastest that anything can travel. So far he has not been proven wrong. EMR can have its wavelength changed if the source is receding or approaching as in the red-shift example of distant galaxies and stars that are moving away from us
25、at very high speeds.The emitted spectral light from these receding bodies appears more red than it would be if the object was not moving away from us. We only have full electronic control over frequencies in the microwave range and lower. Higher frequencies must be created by waiting for the energy
26、to be released from elements as photons. We can either pump energy into the elements (ex. heating a rock with visible EMR and letting it release infrared EMR) or let it naturally escape (ex. uranium decay). We can only see the visible spectrum. All other bands of the spectrum are depicted as hatched
27、 colours. Syst eme International dunit es (SI Units) SymbolNameExp.Multiplier Yyotta10241,000,000,000,000,000,000,000,000 Zzetta10211,000,000,000,000,000,000,000 Eexa10181,000,000,000,000,000,000 Ppeta10151,000,000,000,000,000 Ttera10121,000,000,000,000 Ggiga1091,000,000,000 Mmega1061,000,000 kkilo1
28、031,000 1001 mmilli1030.001 micro1060.000 001 nnano1090.000 000 001 ppico10120.000 000 000 001 ffemto10150.000 000 000 000 001 aatto10180.000 000 000 000 000 001 zzepto10210.000 000 000 000 000 000 001 yyocto10240.000 000 000 000 000 000 000 001 Measurements on this chart SymbolNameValue cSpeed of L
29、ight2.997 924 58 108m/s hPlancks Constant6.626 1 1034Js hPlancks Constant (freq)1.054 592 1034Js fFrequency (cycles / second)Hz Wavelength (meters)m EEnergy (Joules)J Conversions E = hf = c f 1A = 0.1nm 1nm = 10A 1Joule = 6.24 1018eV Gamma Rays Gamma radiation is the highest energy radiation (up to
30、1020eV) that has been measured. At this energy, the radiation could be from gamma-rays, protons, electrons, or something else. Alpha, beta, and delta radiation are not electromagnetic but are ac- tually parts of the atom being released from a radioactive atom. In some cases this can cause gamma radi
31、ation. These are not to be confused with brain waves of similar names. Visible Spectrum The range of EMR visible to humans is also called “Light”.The visible spectrum also closely resembles the range of EMR that fi lters through our atmosphere from the sun. Other creatures see diff erent ranges of v
32、isible light, for example bumble-bees can see ultraviolet light and dogs have a diff erent re- sponse to colours than do humans. The sky is blue because our atmosphere scatters light and the shorter wavelength blue gets scattered the most. It appears that the entire sky is illuminated by a blue ligh
33、t but in fact that light is scattered from the sun. The longer wavelengths like red and orange move straight through the atmosphere which makes the sun look like a bright white ball containing all the colours of the visible spectrum. Interestingly, the visible spectrum covers approximately one octav
34、e. Astronomers use fi lters to capture specifi c wavelengths and reject unwanted wavelengths, the major astronomical (visual) fi lter bands are depicted asX Infrared Radiation Infrared radiation (IR) is sensed by humans as heat and is below the range of human vision. Humans (and anything at room tem
35、perature) are emitters of IR. IR remote control signals are invisible to the human eye but can be detected by most camcorders. Night vision scopes/goggles use a special camera that senses IR and converts the image to visible light. Some IR cameras employ an IR lamp to help illuminate the view. IR LA
36、SERs are used for burning objects. A demonstration of IR is to hold a metal bowl in front of your face. The IR emitted by your body will be refl ected back using the parabolic shape of the bowl and you will feel the heat. LASER LASER is an acronym for Light Amplifi cation by Stimulated Emission of R
37、adiation. A LASER is a device that produces monochromatic EMR of high intensity. With proper equipment, any EMR can be made to operate like a LASER. For example, microwaves are used to create a MASER. Polarization As a photon (light particle) travels through space, its axis of electrical and magneti
38、c fl uctuations does not rotate. Therefore, each photon has a fi xed linear polarity of somewhere between 0to 360. Light can also be circularly and elliptically polarized. Some crystals can cause the photon to rotate its polarization. Receivers that expect polarized photons will not accept photons t
39、hat are in other polarities. (ex. satellite dish receivers have horizontal and vertical polarity positions). A polarized fi lter (like PolaroidTMsunglasses) can be used to demon- strate polarized light. One fi lter will only let photons that have one polarity through. Two overlapping fi lters at rig
40、ht angles will almost totally block the light that exits, however, a third fi lter inserted be- tween the fi rst two at a 45angle will rotate the polarized light and allow some light to come out the end of all three fi lters. Light that refl ects off an electrical insulator becomes polarized. Con- d
41、uctive refl ectors do not polarize light. Perhaps the most reliably polarized light is a rainbow. Moonlight is also slightly polarized. You can test this by viewing the moonlight through a PolaroidTMsunglass lens, then rotate that lens, the moonlight will dim and brighten slightly. Refraction Refrac
42、tion of EMR is dependent on wavelength as can be seen by the prism example below. By using a glass prism, white light can be spread by refraction into a spectrum of its composite colours. All wavelengths of EMR can be re- fracted by using the proper mate- rials. Source Focal point Convex lenses make
43、 objects ap- pear closer and are used to correct far-sitedness. Source Concave lenses make objects ap- pear farther away and are used to correct near-sitedness. Photo by STScI Heavy objects like dense galaxies and large planets cause light to bend due to gravitational lensing. Refl ection Refl ectio
44、n of EMR is dependent on wavelength as demonstrated when visible light and radio waves bounce off objects that X-Rays would pass through. Microwaves, which have a large wavelength compared to visible light, will bounce off metal mesh in a microwave oven whereas visible light will pass through. Source ir Refl ector EMR of any wavelength can be re- fl ected, however, the refl ectivity of a material depends on many fac- tors including the wavelength of the incident beam. The angle of incidence (i) and angle of refl ection (r) are the same. c ? 2003-12-25 RadioFans.CN 收音机爱 好者资料库