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Waves and Sound

Chapter 7: Waves and Sound

Updated Mar 26, 2026
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🎯 Diagnostic: Test Your Starting Level 24 questions (2 per section). No prior reading required, see what you already know.

Aim to answer every question before checking. Missed questions point you to the sections you need most.

1. (7.1) Wave speed, wavelength, and frequency are related by:
C. If the wave speed is fixed (same medium), longer wavelengths correspond to lower frequencies.
2. (7.1) The period T of a wave is:
D. Units of T are seconds; units of f are s⁻¹ = Hz.
3. (7.2) In a transverse wave:
A. Transverse waves can be polarized; longitudinal waves cannot.
4. (7.2) In a longitudinal wave:
B. Pressure compressions and rarefactions alternate along the direction of propagation.
5. (7.3) The superposition principle says:
C. Linear superposition holds for low-amplitude waves; nonlinear effects appear at very high intensities.
6. (7.3) Two waves of equal frequency and amplitude that are in phase:
D. Intensity is proportional to amplitude squared, so doubled amplitude means 4× the intensity.
7. (7.4) A standing wave:
A. Musical instruments, laser cavities, and string resonance all rely on standing waves.
8. (7.4) For a string fixed at both ends, the fundamental frequency is:
B. Half a wavelength fits on the string; tuning a guitar changes L (fret) or v (tension) to change the pitch.
9. (7.5) The speed of sound in air at 20 °C is approximately:
C. Sound travels at about 1500 m/s in water and about 5000 m/s in steel.
10. (7.5) Sound waves are:
D. Sound needs a medium; it cannot travel through a vacuum.
11. (7.6) Sound intensity level in decibels is:
A. Logarithmic scale covers a huge dynamic range that ears and eyes actually experience.
12. (7.6) A 10 dB increase in sound level represents:
B. 20 dB → 100×; 30 dB → 1000×.
13. (7.7) Attenuation of a sound wave refers to:
C. Geometric attenuation gives intensity ∝ 1/r² for a point source.
14. (7.7) Damping of an oscillation refers to:
B. Car shock absorbers are a familiar example of heavy damping.
15. (7.8) The Doppler effect:
A. Used by meteorologists (Doppler radar) and astronomers (redshift).
16. (7.8) An ambulance approaches you at high speed. Its siren sounds:
B. As it passes, the pitch drops suddenly (reversal of relative motion).
17. (7.9) Beats arise when:
A. Piano tuners use beats to match a note to a reference pitch.
18. (7.9) Two tuning forks at 440 Hz and 444 Hz produce beats at:
D. Four beats per second.
19. (7.10) Ultrasound is:
A. Medical ultrasound uses 2-18 MHz frequencies to image soft tissue.
20. (7.10) A sonic boom occurs when:
B. Supersonic aircraft create the characteristic Mach cone behind them.
21. (7.11) Simple harmonic motion is characterized by:
C. The prototypical mass-on-a-spring and small-amplitude pendulum both follow SHM.
22. (7.11) The period of a mass-spring oscillator is:
D. Stiffer spring (larger k) → shorter period; heavier mass → longer period.
23. (7.12) Resonance occurs when:
A. Damping limits the resonant amplitude; undamped resonance would grow without bound.
24. (7.12) A simple pendulum's period depends on:
B. For large-amplitude swings, the period gets slightly longer (small-angle approximation breaks down).

You pluck a guitar string. Within a fraction of a second, the string’s vibration has become a pressure wave rippling through the air, entered your ear canal, vibrated your eardrum, converted into nerve impulses, and registered in your brain as a musical note. The entire chain — from mechanical oscillation to conscious perception — took less time than a blink.

Waves are how energy moves without matter tagging along. A stadium “wave” carries excitement across 50,000 fans, but no fan leaves their seat. Ocean waves carry energy across entire oceans, yet the water molecules mostly bob up and down in place. Sound carries conversations across a room. Light carries images across the universe. Neither one requires any material to physically travel from source to receiver — just a disturbance propagating through a medium (or, in light’s case, through pure vacuum).

The MCAT tests waves heavily because the physics connects to so many biological systems: sound → hearing, ultrasound, echocardiography. Light → vision, microscopy, spectroscopy. Simple harmonic motion → molecular vibrations in IR spectroscopy, oscillations of pressure in blood vessels, even action potentials. Master wave behavior and you’ll reason through passages on topics you’ve never seen before.

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