Study guides › C/P › Physics
Waves & Sound
Waves carry energy through matter and space. You will learn wave properties, interference and beats, standing waves in strings and pipes, sound intensity in decibels, and the Doppler effect, along with the equations that solve each type of problem.
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What this chapter covers
- Wave Properties. Almost every wave question comes back to v = fλ and to knowing which quantities the source sets and which the medium sets.
- Superposition, Interference & Beats. When waves overlap, their displacements add. That single rule explains interference patterns, beats, and reflections.
- Standing Waves in Strings & Pipes. Resonance in strings and air columns is a favorite: know the boundary conditions and the harmonic pattern for each.
- Sound Intensity & Decibels. Decibels are a logarithmic scale, so the MCAT tests whether you can convert between intensity ratios and dB changes.
- The Doppler Effect. Relative motion shifts the pitch you hear. Get the sign rule right and every Doppler problem is a one-line calculation.
Key points to know
- v = fλ; f is set by the source, v by the medium
- Sound is longitudinal and needs a medium; light is transverse
- Overlapping waves add algebraically
- In-phase sources: path difference of mλ is loud, (m + ½)λ is quiet
- Nodes are λ/2 apart; fixed ends and closed ends are nodes
- String and open pipe: f_n = nv/2L, all harmonics
- I = P/A; point sources follow the inverse-square law
- β = 10 log(I/I₀) with I₀ = 10⁻¹² W/m²
Try a practice question
A sound wave travels from air into water. Which quantity stays the same?
- Wavelength
- Speed
- Frequency
- Both wavelength and speed
Show the answer
C. Frequency is fixed by the source. Speed depends on the medium and wavelength changes to match (λ = v/f), so both of those change.
Common questions
What does this chapter cover?
Waves & Sound covers Wave Properties, Superposition, Interference & Beats, Standing Waves in Strings & Pipes, Sound Intensity & Decibels, The Doppler Effect.
What should I know first?
v = fλ; f is set by the source, v by the medium Sound is longitudinal and needs a medium; light is transverse Overlapping waves add algebraically
25 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.