Two tuning forks are struck simultaneously — one at 440 Hz and one at 880 Hz — from 10 meters away. Assuming the same air temperature, which reaches your ears first?
AThe 880 Hz fork, because higher frequency means more energy and faster propagation
BBoth arrive simultaneously, because sound speed depends on the medium, not on frequency
CThe 440 Hz fork, because lower frequency waves have longer wavelengths and travel faster
DThe 880 Hz fork, because it completes more wave cycles per second
Sound speed in a given medium at a given temperature is a fixed property of the medium — it does not depend on frequency or amplitude. Both forks travel at 343 m/s in the same air and arrive simultaneously. Option A represents the common misconception that 'higher frequency = higher speed.' In fact, higher frequency simply means shorter wavelength (since v = fλ and v is fixed), not faster travel.
Question 2 Multiple Choice
A sound wave passes from air into water. Which of the following correctly describes what changes and what stays the same?
AFrequency increases because water molecules vibrate faster
BSpeed increases and wavelength changes, but frequency remains set by the source
CAmplitude increases because water is denser and transfers energy more efficiently
DFrequency and speed both increase proportionally, keeping wavelength constant
When a wave crosses into a new medium, the source still determines how many compressions per second are emitted — frequency is fixed by the source, not the medium. Speed changes (water ~1480 m/s vs. air ~343 m/s) and, since v = fλ, wavelength changes proportionally. This is a direct application of the principle that wave speed is a medium property.
Question 3 True / False
A louder sound (greater amplitude) travels faster through air than a quieter sound of the same frequency.
TTrue
FFalse
Answer: False
Amplitude and speed are independent properties of a sound wave. Amplitude determines loudness (the size of pressure fluctuations), but wave speed is determined entirely by the medium's properties — temperature, density, and elastic modulus. A thunderclap and a whisper at the same temperature travel at exactly the same speed. Confusing amplitude with speed is analogous to confusing how hard you swing with how fast the ripples spread.
Question 4 True / False
Sound waves cannot travel through a vacuum because they require a material medium to propagate their alternating compressions and rarefactions.
TTrue
FFalse
Answer: True
Sound is a mechanical, longitudinal wave — it propagates by particles pushing their neighbors through collisions. Without a medium (no molecules to compress and rarefy), there is nothing to transmit the disturbance. This is why the classic science-fiction trope of loud space explosions is physically wrong: space is (approximately) a vacuum, so no sound can propagate. The bell-jar demonstration — evacuating the jar silences a ringing bell inside — is the canonical experimental proof.
Question 5 Short Answer
Why does sound travel faster in steel (~5000 m/s) than in air (~343 m/s), even when produced by the same source at the same frequency?
Think about your answer, then reveal below.
Model answer: Sound speed depends on the medium's elastic properties and density, not on the source. Steel has much stronger intermolecular bonds than air, so disturbances are transmitted between particles far more quickly. The restoring force in steel is enormous compared to the compressibility of air, enabling the compression-rarefaction cycle to propagate at much higher speed. The source frequency is unchanged — only the speed (and thus wavelength) differs.
The general formula v = √(elastic modulus / density) captures this: steel has a far higher bulk modulus (resistance to compression) relative to its density than air does. This is why dense materials with strong bonds (metals, glass, water) all conduct sound faster than gases. The key insight is that speed is a medium property, entirely separate from the frequency or amplitude that the source determines.