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Sound — Syllabus

Tamil Nadu Board · Class 9 · Science

What Sound covers in Tamil Nadu Board Class 9 Science: 4 topics, for the 2026-27 session. Part of the Tamil Nadu Board Class 9 Science syllabus.

43 questions40 flashcards5 concepts

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A comparison diagram showing two sound waves with different frequencies, illustrating how higher frequency corresponds to higher pitch and lower frequency to lower pitch.
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4 Topics · Tamil Nadu Board Class 9 Science · 2026-27

Topics in Sound

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1. Production and Propagation of Sound

  • Sound is produced by the vibration of objects (e.g., tuning fork, vocal cords, strings of musical instruments).
  • Sound needs a material medium (solid, liquid, or gas) for propagation. It CANNOT travel through vacuum.
  • Bell-Jar Experiment proves sound cannot travel through vacuum: as air is pumped out of the jar containing a ringing bell, the sound becomes fainter and finally disappears.
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2. Characteristics of a Sound Wave

  • A sound wave is completely described by five characteristics: Amplitude, Frequency, Time Period, Wavelength, and Velocity (Speed).
  • Amplitude (A): Maximum displacement of medium particles from rest position. SI unit: metre (m). Larger amplitude → louder sound.
  • Frequency (n): Number of complete vibrations (cycles) per second. SI unit: hertz (Hz) or s⁻¹.
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3. Distinguishing Sounds – Loudness, Pitch, and Timbre

  • Sounds can be distinguished by three qualities: Loudness, Pitch, and Timbre (Quality).
  • LOUDNESS depends on the amplitude of the sound wave. Greater amplitude → louder sound. Loud sound has higher energy and travels farther.
  • Intensity of sound is the amount of energy crossing per unit area per unit time, perpendicular to the direction of propagation. Unit: decibel (dB), named after Alexander Graham Bell.
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4. Speed of Sound

  • Speed of sound is the distance travelled by a sound wave per unit time in an elastic medium.
  • Speed of sound varies with the medium: fastest in solids, slower in liquids, slowest in gases.
  • Speed of sound in air at 0°C = 330 m/s; at 25°C = 340 m/s. Speed increases with increase in temperature.

Key Concepts

Sound is created when an objectSound cannot travel through a vacuumSound waves are longitudinal wavesAmplitude is the maximum displacementFrequency is the number of complete

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Frequently Asked Questions

What are the important topics in Sound for Tamil Nadu Board Class 9 Science?
Key topics in Sound include Production and Propagation of Sound, Characteristics of a Sound Wave, Distinguishing Sounds – Loudness, Pitch, and Timbre, Speed of Sound. Study these first, then practise questions on each for Class 9 exams.
How should I revise Sound for Class 9 exams?
Learn the core ideas first, then work through the 43 practice questions on Sound. Revise definitions regularly and use flashcards for quick recall before the exam.

Sources & Official References

Content is aligned to the official syllabus. Refer to the board website for the latest curriculum.

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All Tamil Nadu Board Class 9 Science Syllabus

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