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Sound — Question 10

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Question 10

When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear an echo sound on a hotter day?

Answer

Speed of sound increases with temperature. Hence, on a hotter day, speed of sound in air will be more.

An echo is heard when the time interval between the reflected sound and the original sound is at least 0.1 seconds.

Therefore, on a hotter day, as speed of sound in air will be more, for same distance, time taken by the reflected sound to reach the ear will be less. As chances of this time interval being less than 0.1 seconds is more so we might not hear an echo sound on a hotter day.

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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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