Měření vlnových délek vlnových vlastností
Wavelength(orcanbeconvertedtofrequency)isanimportantcharacteristicindexofwavesandameasureofwaveproperties.Forexample:mechanicalwavescanbemeasuredfromitswavelength.Theaudiblesoundwavelengthrangesfrom17mmto17m,andthecorrespondingfrequencyisabout20000Hzto20Hz(thefrequencyisinverselyproportionaltothewavelength,sothehigherfrequencyisinthefront);electromagneticwavescanalsobemeasuredbyItismeasuredbyitswavelength.Thevisiblelightofthehumaneyerangesfromadeepredwavelengthof750nmandafrequencyof400THztoapurplewavelengthof400nmandafrequencyof750THz.
AsshowninFigure1arethevariouswavelengthsofelectromagneticwaves:
Whendiscussingthepropagationofelasticwaves,itisassumedthatthemediumiscontinuous,becausewhenthewavelengthismuchlargerthanthatbetweenthemoleculesofthemediumInthedistance,withinadistanceofonewavelengthinthemedium,therearecountlessmoleculesvibratingoneafteranother.Macroscopically,themediumseemstobecontinuous;butifthefrequencyofthewavesourceisextremelyhighandthewavelengthisextremelysmall,whenthewavelengthisassmallasorlessthanWhentheintermoleculardistanceisoftheorderofmagnitude,betweentwomoleculesthatareaboutonewavelengthapart,therearenoothermolecules,andthemediumcannolongerbeconsideredcontinuous,andelasticwavescannolongerbepropagated.Thedistancebetweenmoleculesinahighvacuumissogreatthatmechanicalwavescannotbepropagatedforthisreason.
Vlnové délky příčných a podélných vln
Wavelengthreferstothedisplacementbetweentworelativeequilibriumpositionsinthewavepatternalongthepropagationdirectionofthewave.Themeaningsofthewavelengthsoftransverseandlongitudinalwavesaredifferent.Intransversewave,wavelengthreferstothedistancebetweentwoadjacentpointswithphasedifference,usuallyadjacentwavecrests,troughsorcorrespondingzerocrossingpoints.Inlongitudinalwaves,thewavelengthreferstothedistancebetweentwoadjacentdenseorsparseparts.Thewavelengthisoftenexpressedasλinphysics,andtheinternationalunitismeter(m).
Vztah mezi vlnovou délkou a frekvencí
Frequencyisthenumberofwavespassingthroughacertainplacewithinafixedtime,namely.Therefore,fromtheexpressionofthepreviouswavelength,therelationshipbetweenwavelengthandfrequencycanbeobtainedas:
ThepropagationintheequationTheunitofspeedism/s(meterspersecond),theunitoffrequencyishertz(Hz,referredtoashertz),andtheunitofwavelengthisMeter.Forexample,thefirstprogramoftheCentralPeople’sBroadcastingStationusesabroadcastingfrequencyof639kHz(kilohertz),andthepropagationspeedofelectromagneticwavesintheairis3×108m/s,thenitcanbecalculatedasTheradiowavewavelengthofthisprogramis:
Vztah mezi elektromagnetickými vlnami
TherelationshipbetweenelectromagneticwavelengthandenergyTheformulais
Intheformula,Erepresentsenergy,andhisPlanck'sconstant;cisthespeedoflightinvacuum,approximately2.998x108m/s.
Therelationshipbetweenelectromagneticwavelengthandfrequencyis
Wherecisthespeedoflight,isthewavelength,andisthefrequencyoftheelectromagneticwave.