Modelová Otázka ID 3253 - 
Které z následujících tvrzení správně popisuje akustické vlnění o vlnové délce ve vzduchu λ = 3 300 m za normálních podmínek?
Správná odpověď je: B
Ve vzduchu je za normálních podmínek rychlost zvuku přibližně 330–340 m · s−1. Pro určení periody vlnění lze jednu vlnovou délku považovat za dráhu pohybu vlny. Pro dobu tohoto pohybu odpovídající periodě platí 
, tedy:
T = λ/v = 3 300 m/330 m · s−1 = 10 s.
Perioda tohoto vlnění je tedy 10 s. Pro frekvenci pak platí:
f = 1/T= 1/10 s = 0,1 s−1 = 0,1 Hz.
Vlnění má nižší frekvenci než zvuk, jedná se tedy o infrazvuk.
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