physics

PhysicsNotes:EMspectrum:rangeofEMwavesinorderofincreasingfrequency Characteristics:EMwavesaretransversewaves,cantravelviavacuumatsamespeed3.0x10 ⁸m/sThelongerthewavelength,thelowerthefrequency,thelowertheenergy,viceversa.ThedirectionofoscillationisPERPENDICULARtothedirectionofwavetravel(transversewaves).

Utility:RADIOtelescopesstudytheradiofrequencyportionoftheelectromagneticspectrumemittedbyastronomicalobjects,suchasstars.RadiowavesproducedbyoscillatingelectriccurrentsinatransmittingantennaispickedbyradioandTVaerialsatthereceivingend. MICROWAVESofaparticularfrequencyarereadilyabsorbedbywatermolecules.Almostallfoodcontainswater,sofoodcanbeheatedquicklyinamicrowaveoven.Aradarsendsoutmicrowaves,whichgetreflectedbyotherobjects.Whenthesereflectedsignalsaredetected,theradaroperatorwillgeta'picture'ofthesurroundings.Whenusingasatellitephonenetworktomakeanoverseascall,microwavesignalsaresentouttospacebyalargeaerialdishtosatellitesorbitingtheearth.Thesesatellitesthenrelaythesignalstothereceivingdishoverseas. AdvancedsecuritysystemsusepassiveINFRARED(PIR) motiondetectors.Thesesensors"see"theinfraredenergyemittedbyanintruder'sbodyheat.Whenanintruderwalksintothefieldofviewofthedetector,thesensordetectsasharpincreaseininfraredenergy.Thetransmitterintheremotecontrolhandsetsendsoutpulsesofinfraredlightwhentheuserpressesabutton.Eachbuttonhasauniquepatternofinfraredpulses. Areceiverinthedevicerecognizesthispattern,causingthedevicetorespondaccordingly.Infraredcamerasdetectinfraredenergy(heat)andconvertsitintoanelectronicsignal.Thesignalsareprocessedtoproduceathermal imageonavideomonitor. Lightwavelength:

Intelecommunication, digital signalsaresentthroughopticalfibresusingshortpulsesofLIGHT.Inmedicine,lasersareusedtoseal bloodvessels.Inindustry,lasersareusedtoweldmetalstogether. ProlongedexposuretoUVraysincreasesyourriskofdevelopingskincancer.ThisisbecauseUVrayscarriesenoughenergytoremoveelectronsfromatomsormolecules,therebyionizingthem.LivingcellsandtissuecanbedamagedbyUVradiation.UVcounterfeitcurrencydetectorsareusedtodetectspecialinksinthebillsthatonlyappearundertheproperwavelengthofUVlight.SunbedsworkbyexposingtheskintoUVradiation,similartothatfoundinsunshine.Thisreleasesachemicalwhichcausestheskintotan.UVsterilizerusesUVlightthatkillsmicroorganismsthatgothroughitbyalteringanddamagingtheirDNA. LivingcellsandtissuecanbedamagedbyX-rays.ThisisbecauseX-rayscarryenoughenergytoremoveelectronsfromatomsormolecules,therebyionizingthem.OverexposuretoX-rays

increasestheriskofdevelopmentalproblemsandcancer.Theriskofradiationisgreatertoafetus,sopregnantpatientsareadvisedtoavoidexposuretoX-rays.WhenabeamofX-raysstrikeacrystal,thecrystallineatoms"spread"theX-raysintomanyspecificdirections.Thepatternofthe"spread"canbestudiedtounderstandthecrystalstructure.AftertheX-rayspassthroughthebaggage,theyarepickedupbyadetector.The"picture"formedonthemonitorisusedbyairportstafftodetermineiftherearedangerousitemsinthebaggage.Onaphotographicfilm,darkareasshowwheretheX-rayshavepassedthr