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Sound — Question 13

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Question 13

A sound wave travels at a speed of 339 ms-1. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?

Answer

Given,

Speed of sound (v) = 339 ms-1

Wavelength of sound (λ) = 1.5 cm

Converting cm to m

100 cm = 1 m

1.5 cm = 1.5100\dfrac{1.5}{100}= 0.015 m

We know,

Speed (v) = Wavelength (λ) x Frequency (ν)

or

Frequency (ν) = Speed (v)Wavelength (λ)\dfrac{\text{Speed (v)}}{\text{Wavelength (λ)}}

Substituting we get,

ν = 3390.015\dfrac{339}{0.015} = 22,600 Hz

Hence, the frequency of the sound = 22,600 Hz

No, it will not be audible as it is outside the audible range for human ear i.e. 20 Hz to 20,000 Hz.

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Science | Chapter 11: SoundWeb Content — Quick Reference

Chapter 11: Sound — Quick Reference

longitudinal wave frequency wavelength echo SONAR ultrasound human ear speed of sound

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
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