Sound is an essential part of our daily life. It allows us to communicate, enjoy music, and understand our surroundings. In physics, sound is studied as a mechanical wave that travels through different mediums like air, water, and solids. Understanding sound not only helps students excel in exams but also gives insights into practical applications such as medical imaging, acoustics in halls, and controlling noise pollution.
This chapter covers all the important aspects of sound, including:
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Sound Waves – How sound is produced, transmitted, and the nature of longitudinal waves.
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Characteristics of Sound – Concepts like pitch, loudness, and quality of sound.
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Reflection of Sound (Echo) – How echoes are formed and their practical uses.
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Speed of Sound – Factors affecting the speed in different mediums.
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Noise Pollution – Causes, effects, and preventive measures.
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Importance of Acoustics – Designing auditoriums, halls, and studios for better sound.
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Audible Frequency Range – The range of frequencies humans can hear.
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Ultrasound – Applications in medicine, industry, and scientific research.
This guide is prepared to help students master all key concepts, practice MCQs, short questions, and long questions, and perform well in board exams.
Important MCQs – Unit 11 Sound
1. Which is an example of a longitudinal wave?
(a) Sound wave ✅
(b) Light wave
(c) Radio wave
(d) Water wave
2. Which form of energy is sound?
(a) Electrical
(b) Mechanical ✅
(c) Thermal
(d) Chemical
3. For a normal person, audible frequency range for sound wave lies between
(a) 10 Hz and 10 kHz
(b) 20 Hz and 20 kHz ✅
(c) 25 Hz and 25 kHz
(d) 30 Hz and 30 kHz
4. The distance between two consecutive compressions is called:
(a) Frequency
(b) Amplitude
(c) Wavelength ✅
(d) Pitch
5. The formula used to calculate the speed of sound is:
(a) v = f + λ
(b) v = f / λ
(c) v = f × λ ✅
(d) v = λ / f
Short Questions – Unit 11 Sound
1. What is a sound wave and how is it produced?
Answer:
A sound wave is a type of mechanical wave produced by a vibrating body. When the body vibrates, it causes the particles of the surrounding medium (air, water, or solid) to vibrate as well. These vibrations create compressions and rarefactions that travel through the medium. When these waves reach our ears, we hear them as sound.
Key Points for Exams:
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Mechanical wave – needs a medium
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Produced by vibrating bodies
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Involves compressions and rarefactions
2. Define loudness of sound.
Answer:
Loudness is the property of sound by which we can distinguish between loud and faint sounds. It depends on the amplitude of the vibrating body – the greater the amplitude, the louder the sound.
Key Points:
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Determines how strong or soft a sound appears to the ear
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Directly related to amplitude of vibration
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Measured in decibels (dB)
3. What is meant by reflection of sound?
Answer:
The reflection of sound is the bouncing back of sound waves when they strike a hard surface. This reflected sound can be heard as an echo if the distance is sufficient.
Key Points:
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Occurs when sound hits a hard and smooth surface
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Produces an echo if the reflected sound is distinct
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Used in sonar, ultrasound, and designing auditoriums
4. Define intensity of sound.
Answer:
Intensity of sound is the sound energy passing per second through a unit area, perpendicular to the direction of sound propagation.
Key Points:
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Determines how strong or weak a sound is
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Depends on the amplitude of vibration
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Measured in watts per square meter (W/m²)
Long Questions – Unit 11 Sound
Question: What is the necessary condition for the production of sound?
Introduction:
Sound is a form of energy that travels through a medium in the form of waves. It helps us communicate and hear various sounds around us.
Necessary Condition for Sound Production:
The essential condition for the production of sound is vibration.
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Sound is always produced by a vibrating body.
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When an object vibrates, it causes the surrounding medium (like air) to vibrate as well.
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These vibrations travel in the form of compressional (longitudinal) waves, which reach our ears and are interpreted as sound.
Examples of Sound Produced by Vibrations:
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Vibrating Strings (Guitar):
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When a guitar string is plucked, it vibrates.
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The vibrations travel through air and produce sound.
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Vibrating Vocal Cords:
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In humans, vocal cords vibrate when we speak.
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These vibrations generate sound waves that travel through air.
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Tuning Fork (Lab Activity):
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When a tuning fork is struck with a rubber hammer, its prongs vibrate.
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Touching a suspended plastic ball to the prongs makes the ball move—proving the fork is vibrating.
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Dipping the vibrating fork in water creates splashing, showing the vibrations.
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Scientific Explanation:
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Vibrations cause compressions (high-pressure regions) and rarefactions (low-pressure regions) in air molecules.
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These alternating regions travel as longitudinal waves to reach our ears.
Summary:
Hence, the vibration of a body is the essential condition for the production of sound. Without vibration, no sound can be produced.
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