vlnová délka

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.

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