Waves and Sound
Read wave evidence, connect speed, frequency, and wavelength, and distinguish pitch, loudness, and propagation speed.
Waves and Sound
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A wave transfers energy while the medium’s particles oscillate around their positions
Use frequency for cycles per second, period for time per cycle, wavelength for the length of one complete pattern, and amplitude for maximum displacement from equilibrium. For sound, frequency controls pitch while amplitude is related to intensity and perceived loudness.
Do not mix up wave quantities
In a fixed medium, changing frequency changes wavelength—not the propagation speed.
Sound needs a medium
Sound is a longitudinal mechanical wave in air; electromagnetic waves can cross a vacuum.
Identify what changes → hold the medium constant → use one relationship
Problem: Frequency doubles while a wave stays in the same medium.
Recognize: The medium keeps wave speed constant.
Do it fast: From v=fλ, doubling f makes λ half as large.
Why it works
This prevents the most common error: assuming every visible or audible change also changes wave speed.
Five forms you should recognize
At 12 Hz and wavelength 2 m, v=24 m/s.
Higher-frequency sound is heard as higher pitch.
Greater amplitude usually means greater intensity.
Divide the round-trip distance by 2.
A system responds strongly near its natural frequency.
Check before you commit
- Using crest-to-trough as amplitude
- Forgetting the echo round trip
- Assuming louder means faster
- Confusing pitch with loudness
- Changing frequency but keeping wavelength fixed in one medium
- Saying sound travels through a vacuum
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Foundations
Build the core procedure with immediate explanations.
Core Practice
Use mixed forms with less scaffolding.
UPCAT-Style Transfer
Apply the competency in unfamiliar representations.
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Waves and Sound FAQ
Does a louder sound travel faster?
Not under ordinary conditions in the same medium; loudness mainly reflects intensity.
Why does pitch change when a source moves?
The Doppler effect changes the arrival spacing and observed frequency of wavefronts.
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