Sound Class 9 Notes Science Chapter 11

Introduction

• Sound is a form of energy causing a hearing sensation.
• Other energy forms include mechanical and light energy.
• Energy conservation is the transformation, not creation or destruction, of energy.
• Sound production involves energy utilization.

Production of Sound

• Sound is generated by vibrations (e.g., clapping hands).
• Various methods produce sound: plucking, scratching, blowing, etc.
• Vibrations in vocal cords produce human voice.
• Sound in musical instruments comes from specific vibrating parts.

Propagation of Sound

• Sound travels through mediums (solid, liquid, gas).
• It involves particle vibrations in the medium, which transmit the sound.
• Waves: Disturbances moving through mediums.
• Sound waves: Mechanical waves characterized by particle motion.
• Common medium: Air.
• Sound propagation involves compressions (high pressure) and rarefactions (low pressure).

Sound Waves as Longitudinal Waves

• In longitudinal waves, particle movement is parallel to wave propagation.
• Slinky example demonstrates longitudinal wave properties.

Characteristics of a Sound Wave

• Frequency: Number of oscillations per unit time (Hertz).
• Amplitude: Maximum disturbance magnitude in the medium.
• Speed: Distance a point on the wave travels per unit time.
• Loudness related to amplitude, pitch to frequency.
• Timbre: Quality differentiating sounds with same pitch and loudness.

Speed of Sound in Different Media

• Speed varies with medium and temperature.
• Faster in solids, slower in gases.
• Increases with temperature.

Reflection of Sound

• Sound reflects off surfaces like light, obeying the laws of reflection.
• Requires a large obstacle for effective reflection.
• Example activities demonstrate sound reflection.

Range of Hearing

• Human audible range: 20 Hz to 20 kHz.
• Infrasound: Below 20 Hz.
• Ultrasound: Above 20 kHz.
• Age and species affect hearing range.

Applications of Ultrasound

• Industrial cleaning.
• Detecting metal flaws.
• Medical imaging (echocardiography, ultrasonography).
• Kidney stone treatment.

Key Learnings

• Sound is a longitudinal wave in a medium.
• Speed of sound is influenced by medium and temperature.
• Reflection leads to echoes and reverberation.
• Human hearing has a specific frequency range.
• Ultrasound has diverse applications in healthcare and industry.