I keep getting “Wave speed, frequency and wavelength” questions wrong in Waves & Sound. What's the trap?
saying frequency changes when a wave enters another medium.
The usual trap: saying frequency changes when a wave enters another medium. How to avoid it: source keeps frequency; medium sets speed; wavelength adapts. Go back to the definition — A travelling wave carries energy while the medium's particles oscillate around equilibrium. Its speed is v = f lambda; the source fixes frequency, while the medium fixes wave speed, so wavelength adjusts when the medium changes.
Key point
Wave speed, frequency and wavelength
Common mistake
saying frequency changes when a wave enters another medium.
Memory tip
source keeps frequency; medium sets speed; wavelength adapts.
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