Class 9 Science Chapter 10 Sound Waves: Characteristics and Applications – Revision Notes

Sound Waves: Characteristics and Applications follows sound from how it’s produced to how fast it travels through solids, liquids, and gases, and this page notes the difference between an echo and reverberation along the way.

Last Updated: September 23, 2026

Production and Propagation

• Sound: produced by vibration, travels as a longitudinal wave (compressions + rarefactions).
• Needs a medium; cannot travel through vacuum.

Characteristics

• Wavelength: distance between consecutive compressions/rarefactions.
• Frequency: oscillations/second (Hz); determines pitch.
• Time period: T = 1/frequency.
• Amplitude: max displacement; determines loudness.
• Speed = wavelength × frequency.

Speed in Media

• Solids > liquids > gases (closer particles = faster transfer).

Echo / Reverberation / Echolocation

• Echo: distinct reflected sound; needs ≥17 m reflecting distance.
• Reverberation: persistence from overlapping reflections in enclosed spaces.
• Echolocation: using echoes to detect objects (bats, dolphins, SONAR).

One-Line Summary

Sound is a longitudinal wave needing a medium, described by wavelength, frequency (pitch), and amplitude (loudness), travelling fastest through solids, and its reflection produces echoes, reverberation, and echolocation.

Frequently Asked Questions

Why can sound not travel through a vacuum?
Sound is a mechanical wave that travels by vibrating the particles of a medium such as air, water, or a solid; since a vacuum has no particles to vibrate and carry the disturbance forward, sound cannot travel through it.

What is the difference between the pitch and loudness of a sound?
Pitch depends on the frequency of the sound wave, with a higher frequency producing a higher pitch, while loudness depends on the amplitude of the wave, with a larger amplitude producing a louder sound.

Written by Satish

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