Sound
Vibrations of a source (e.g., loudspeaker cone) produce sound waves that travel through a material medium as longitudinal waves. :contentReference[oaicite:5]{index=5}
Core Properties
- Caused by vibrations of the source.
- Longitudinal — particles oscillate along direction of wave. :contentReference[oaicite:6]{index=6}
- Requires a medium; cannot travel through vacuum. :contentReference[oaicite:7]{index=7}
- Travels through solids, liquids, gases (fastest in solids, slowest in gases). :contentReference[oaicite:8]{index=8}
Compressions & Rarefactions
The wave consists of alternating compressions and rarefactions. As the cone moves forward it creates compressions; backward motion creates rarefactions. :contentReference[oaicite:9]{index=9}
Wave Quantities
- Amplitude ↔ loudness (bigger amplitude → louder). :contentReference[oaicite:10]{index=10}
- Frequency ↔ pitch (higher frequency → higher pitch). :contentReference[oaicite:11]{index=11}
v = f × λ(speed = frequency × wavelength)
Typical Speeds
| Medium | Order / Value | Notes |
|---|---|---|
| Air | ≈ 343 m/s | Increases with temperature. :contentReference[oaicite:12]{index=12} |
| Water | ≈ 1450–1498 m/s | Faster than in air. :contentReference[oaicite:13]{index=13} |
| Solids | Fastest | solid > liquid > gas (speed order). :contentReference[oaicite:14]{index=14} |
Measuring Speed of Sound (Flash–Bang Method)
- Start stopwatch at the flash and stop at the bang. Distance / time = speed. :contentReference[oaicite:15]{index=15}
- Improve accuracy: increase distance, repeat trials, use precise timer. :contentReference[oaicite:16]{index=16}
Ultrasound (and Infrasound)
- Ultrasound — medical imaging (prenatal scans), flaw detection in metals, sonar. :contentReference[oaicite:17]{index=17}
- Infrasound — not in syllabus; very low-frequency sound. :contentReference[oaicite:18]{index=18}
Echoes
- An echo is a reflection of sound. Hard, smooth surfaces reflect; soft, rough surfaces absorb/scatter. :contentReference[oaicite:19]{index=19}
- Reduce unwanted echoes: soft coverings (absorb) or uneven walls (scatter). :contentReference[oaicite:20]{index=20}
Handy Equations
v = f × λ distance (to wall) = (v × time delay) / 2
Loudness & Pitch
| Quantity | Wave Feature | Effect |
|---|---|---|
| Loudness | Amplitude | Bigger amplitude → louder; smaller → quieter. :contentReference[oaicite:21]{index=21} |
| Pitch | Frequency | Higher frequency → higher pitch; lower → lower pitch. :contentReference[oaicite:22]{index=22} |
Exam Tips
- State that sound does not travel in a vacuum.
- Relate loudness ↔ amplitude, pitch ↔ frequency (don’t mix them!).
- Quote sensible orders of speed: solids > liquids > gases. :contentReference[oaicite:23]{index=23}
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