Sound Waves Characteristics and Applications — Class 9 Science NCERT Solutions (Free)

Free step-by-step NCERT solutions for Class 9 Science chapter "Sound Waves Characteristics and Applications" — 8 important questions with detailed answers for CBSE board exam preparation.

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TL;DR: Free step-by-step NCERT solutions for Class 9 Science chapter "Sound Waves Characteristics and Applications" — 8 important questions with detailed ans…

Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated Jul 23, 2026

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Key Questions Covered:

Define sound and explain how sound is produced and propagated.
Define and explain pitch. How is pitch related to frequency?
Define and explain loudness. What factors affect loudness?
Define reflection of sound. What are the laws of reflection of sound?
Define echo and reverberation. Distinguish between them.
What is SONAR? How does it work? Give applications.
+ 2 more questions in the full chapter

Solutions Summary:

Question	Status
Define sound and explain how sound is produced and propag…	✓ Solved
Define and explain pitch. How is pitch related to frequency?	✓ Solved
Define and explain loudness. What factors affect loudness?	✓ Solved
Define reflection of sound. What are the laws of reflecti…	✓ Solved
Define echo and reverberation. Distinguish between them.	✓ Solved
What is SONAR? How does it work? Give applications.	✓ Solved

Showing 6 of 8 questions

Q1: Define sound and explain how sound is produced and propagated.

Sound = Mechanical wave produced by vibrating object; requires medium (air, water, solid) to propagate. Production: Vibrating object causes surrounding medium particles to oscillate, creating disturbance. Propagation: Disturbance travels through medium as longitudinal wave (particles oscillate parallel to direction of wave motion). Example: Tuning fork vibrates → air molecules vibrate → sound propagates Sound CANNOT travel in vacuum (no medium to vibrate)

Q2: Define and explain pitch. How is pitch related to frequency?

Pitch = Characteristic of sound that makes it "high" or "low" to listener. Pitch depends on frequency (f) of vibrating source: • Higher frequency → Higher pitch (shrill sound, like whistle) • Lower frequency → Lower pitch (deep sound, like bass) Frequency (f) = Number of vibrations per second (Hz) Human hearing range: 20 Hz to 20,000 Hz (20 kHz) Sounds below 20 Hz = Infrasound; above 20 kHz = Ultrasound Example: Violin (high pitch) has higher frequency than drum (low pitch)

Q3: Define and explain loudness. What factors affect loudness?

Loudness = Characteristic of sound that makes it "loud" or "soft" to listener; depends on intensity/amplitude. Intensity (I) = Power per unit area = Energy per unit time per unit area (W/m²) Amplitude (A) = Maximum displacement of particle from mean position Factors affecting loudness: (1) Amplitude: Greater amplitude → Louder sound (2) Distance from source: Closer → Louder sound (3) Area of vibrating object: Larger area → Louder sound Loudness measured in decibels (dB) 0 dB ...

Q4: Define reflection of sound. What are the laws of reflection of sound?

Reflection of sound = Sound wave bounces back from hard surface without passing through. Laws of reflection of sound (same as light): (1) Angle of incidence = Angle of reflection (measured from normal) (2) Incident ray, reflected ray, normal all lie in same plane Conditions for reflection: • Surface must be hard and rigid (not absorbing) • Size of surface >> wavelength of sound Applications: Echo, reverberation, design of concert halls, stethoscope

Q5: Define echo and reverberation. Distinguish between them.

Echo = Repeated sound heard distinctly after original sound; reflection of sound from distant hard surface. Condition for echo: Time gap between original and reflected sound ≥ 0.1 s Distance for echo = (v × t)/2 ≥ (343 × 0.1)/2 = 17.15 m (in air at room temp) Reverberation = Prolonged persistence of sound due to multiple reflections from various surfaces. Sound heard as continuous buzz (reflections arrive rapidly, <0.1 s intervals). Distinction: Echo = distinct delayed sound; Reverberation = ...

Q6: What is SONAR? How does it work? Give applications.

SONAR = Sound Navigation And Ranging; uses sound waves to locate and measure distance of underwater objects. Working principle: (1) Transmit ultrasound pulse into water (2) Pulse reflects from object (ship, submarine, sea bed) (3) Receiver detects reflected signal (4) Distance = (v × t)/2, where t = time for round trip, v = speed in water (≈1500 m/s) Applications: • Detecting submarines and ships • Finding depth of sea • Fishing (detecting fish schools) • Navigation underwater

Showing 6 of 8 questions. Visit the full page for complete solutions.