๐ Chapter Overview
Sound is a form of energy produced by vibrating objects. It travels as longitudinal waves through solids, liquids and gases. The chapter covers production and propagation of sound, characteristics of sound (pitch, loudness, quality), speed of sound, applications like echo and SONAR, and the human ear as a detector of sound.
Wave type: Longitudinal
Key formula: v = f ร ฮป
Speed of sound in air โ 343 m/s (at 20ยฐC)
Quick idea: Sound needs a medium; it cannot travel through vacuum. Denser media generally transmit sound faster.
๐ Key Points
- Production: Sound is produced by vibrating objects (strings, vocal cords, tuning fork).
- Propagation: Sound travels as longitudinal waves (compressions and rarefactions).
- Characteristics: Pitch (frequency), Loudness (amplitude), Quality/Timbre (waveform).
- Speed: Depends on medium and temperature (air < liquids < solids typically).
- Echo: Reflection of sound; heard if reflected sound arrives after 0.1 s (minimum) โ distance rule: d = v ร t/2.
- SONAR and echolocation use reflected sound for distance measurement.
- Human ear parts: Outer ear (pinna), eardrum, middle ear (ossicles), inner ear (cochlea).
๐ Formulae & Relations
| Quantity | Symbol/Relation | Typical Value / Unit |
|---|---|---|
| Speed of sound | v = f ร ฮป | m/s |
| Frequency | f (number of vibrations per second) | Hz |
| Wavelength | ฮป (distance between successive compressions) | m |
Example: If a sound has frequency 256 Hz and wavelength 1.33 m, speed = 256 ร 1.33 โ 341 m/s.
๐งช Applications & Examples
| Application | What it uses | Example |
|---|---|---|
| Echo/Reflection | Reflection of sound | Hearing echo in canyon |
| SONAR | Echo for distance measurement | Submarine detection |
| Echolocation | Animal-produced sound reflections | Bats & dolphins |
| Musical instruments | Controlled vibrations | Guitar, flute |
๐ 30 Important Questions & Answers
Q1. What is sound?
Sound is a form of energy produced by vibrating objects and transmitted through a medium as longitudinal waves.
Q2. Can sound travel through vacuum?
No. Sound requires a material medium (solid, liquid, or gas) to travel; it cannot travel through vacuum.
Q3. What type of wave is sound?
Longitudinal wave (particle oscillation parallel to direction of wave propagation).
Q4. Define frequency of sound.
Frequency is the number of vibrations or oscillations per second; measured in hertz (Hz).
Q5. Define wavelength.
Wavelength is the distance between two successive compressions or rarefactions in a sound wave.
Q6. State the relation between speed, frequency and wavelength.
v = f ร ฮป (speed = frequency ร wavelength).
Q7. Approximate speed of sound in air at 20ยฐC?
Approximately 343 m/s.
Q8. How does temperature affect speed of sound in air?
Speed of sound in air increases with temperature.
Q9. What is pitch?
Pitch is how high or low a sound seems; it depends on frequency (higher frequency โ higher pitch).
Q10. What is loudness?
Loudness refers to the magnitude of sound perceived and depends on amplitude and distance from source.
Q11. What is quality (timbre) of sound?
Quality or timbre distinguishes sounds of the same pitch and loudness produced by different sources (e.g., violin vs flute).
Q12. Explain echo.
Echo is the reflection of sound from a surface that is heard after the original sound; must reach listener after at least 0.1 s delay.
Q13. How to calculate minimum distance for hearing an echo in air?
If v โ 343 m/s and minimum time is 0.1 s, distance to reflecting surface โ v ร t / 2 โ 17.15 m.
Q14. What is SONAR?
SONAR (Sound Navigation and Ranging) uses sound pulses and their echoes to detect objects underwater and measure distances.
Q15. Give one example of echolocation in animals.
Bats emit ultrasonic sounds and use echoes to find insects in the dark.
Q16. Which part of ear vibrates first when sound reaches it?
Eardrum (tympanic membrane) vibrates first on receiving sound waves.
Q17. Name the small bones in middle ear.
Malleus (hammer), incus (anvil), and stapes (stirrup).
Q18. Where are sound signals converted into nerve impulses?
In the cochlea of the inner ear; hair cells convert vibrations into electrical signals sent to the brain.
Q19. What is ultrasound?
Sound waves with frequency greater than 20,000 Hz (above human hearing range); used in medical imaging and industrial inspection.
Q20. What is infrasound?
Sound waves with frequency below 20 Hz (below human hearing); used by some animals and in geophysical studies.
Q21. How is noise different from musical sound?
Musical sound has definite pitch, quality and regular wave pattern; noise is irregular and unpleasant.
Q22. Give one method to reduce noise pollution.
Use noise barriers, soundproofing, and reduce loud activities during quiet hours.
Q23. Why do sound waves travel faster in solids than in gases?
Particles in solids are closer and interact more quickly, allowing faster transmission of vibrations.
Q24. A tuning fork of frequency 512 Hz produces waves of speed 340 m/s. Find its wavelength.
ฮป = v/f = 340 / 512 โ 0.664 m.
Q25. What is reverberation?
Multiple reflections of sound in an enclosed space causing prolonged sound; architects reduce it using absorbent materials.
Q26. How do bats avoid collisions while flying at night?
By emitting ultrasonic calls and interpreting the returning echoes (echolocation).
Q27. Which part of an instrument determines pitch?
The frequency produced by the vibrating element (e.g., string length/tension or air column length) determines pitch.
Q28. What is the audible range of human hearing?
Approximately 20 Hz to 20,000 Hz for a young healthy person.
Q29. Why do distant thunder sounds seem lower in pitch sometimes?
Atmospheric absorption and lower frequencies travel farther, making distant thunder sound lower and more muffled.
Q30. Why should loud sounds be avoided for long durations?
Prolonged exposure to loud sounds can damage hair cells in the ear, leading to hearing loss.