6
Question Question 6
A person has a hearing range from 20 Hz to 20 kHz. What are the typical wavelengths of sound waves in air corresponding to these two frequencies? Take the speed of sound in air as 344 ms-1.
Given,
Speed (vair) = 344 ms-1
We know,
Speed (v) = Wavelength (λ) x Frequency (ν)
or
Wavelength (λ) =
(a) For ν = 20 Hz, substituting we get,
λ1 = = 17.2 m
(b) For ν = 20,000 Hz, substituting we get,
λ2 = = 0.0172 m
Hence, typical wavelengths of sound waves in air corresponding to 20 Hz and 20,000 Hz are 17.2 m and 0.0172 m respectively.
BRIGHT TUTORIALS
BRIGHT TUTORIALS
CBSE Class IX | Academic Year 2026-2027
9403781999
Excellence in Education
Science | Chapter 11: SoundWeb Content — Quick Reference
Chapter 11: Sound — Quick Reference
Quick Revision Points
- Sound: produced by vibration, needs medium, longitudinal wave (compressions + rarefactions)
- v = fλ; Speed in air ≈ 344 m/s; Solids > Liquids > Gases
- Loudness → amplitude; Pitch → frequency; Quality → waveform
- Echo: reflected sound; min distance = 17.2 m (at v = 344 m/s, t ≥ 0.1 s)
- Audible range: 20 Hz – 20 kHz; Infrasound < 20 Hz; Ultrasound > 20 kHz
- SONAR: d = vt/2; Human ear: pinna → canal → eardrum → hammer/anvil/stirrup → cochlea → auditory nerve
Exam Tips for Chapter 11
- Read the detailed chapter notes for complete coverage of all NCERT topics.
- Practice all NCERT in-text and back exercise questions — they are frequently asked in exams.
- Focus on comparison tables, diagrams, and definitions — these are high-scoring areas.
- For numericals (if applicable), practice at least 20 problems of varying difficulty.
- Refer to the practice question bank (200+ questions) for thorough preparation.
Related Resources
- Detailed Notes: ch11-sound.html
- Practice Questions: 100+ questions with answers in 05-practice-questions/
- Chapter Test: 30-mark test paper in 06-tests/chapter-tests-30marks/
- Formula Sheet: Complete formula reference in 03-teacher-aid/formula-sheet.html