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Sound

Tamil Nadu Board · Class 9 · Science

Quick revision notes for Sound — Tamil Nadu Board Class 9 Science. Key concepts, formulas, and definitions for last-minute revision.

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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Key Topics to Revise

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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.

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Full Notes

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

Frequently Asked Questions

What are the important topics in Sound for Tamil Nadu Board Class 9 Science?
Key topics in Sound include Sound – Complete Chapter Overview, Sound: Comprehensive Concept Overview, This flowchart shows the step-by-step process of how sound is produced when a tuning fork is struck and how it travels to the ear.. These are the concepts Tamil Nadu Board Class 9 examiners draw on most — study them first, then practise related questions.
How to score full marks in Sound — Tamil Nadu Board Class 9 Science?
Understand the core concepts first, then work through the 43 practice questions available for this chapter. Revise formulas and 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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