Chapter 11: Sound Case Study Questions | science Class 9 CBSE

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Chapter 11: Sound Case Study Questions | science Class 9 CBSE | ByteNotes.in

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Case Set 1

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Ravi notices that when he plucks a stretched rubber band, it vibrates and produces sound. His science teacher explains how sound is related to vibration.

Question 1: Q1. What causes the sound in this case?

Sound is produced due to vibrations of the rubber band.
When plucked, the rubber band moves back and forth rapidly.
These vibrations create disturbances in the air, generating sound.

Question 2: Q2. Can vibrations be seen or felt?

Yes, in some cases vibrations can be seen or felt.
If the object is large or vibrating slowly, the motion is visible.
In musical instruments, strings visibly vibrate when struck or plucked.

Question 3: Q3. What is the essential condition for production of sound?

Vibration of an object is necessary to produce sound.
Without vibration, no sound can be generated.
All sound-producing objects vibrate.

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Case Set 2

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During a science experiment, a tuning fork is struck and brought near a bowl of water. When dipped, it splashes water, even though no object touches the bowl.

Question 1: Q1. Why does water splash when tuning fork is dipped?

The prongs of the tuning fork are vibrating rapidly.
These vibrations transfer to water, causing it to splash.
This shows that the tuning fork is producing sound via vibration.

Question 2: Q2. Why can't we always see the fork vibrating?

Because the tuning fork vibrates at high frequency.
Human eyes can’t detect such rapid motion.
But effects like splashing or humming indicate vibration.

Question 3: Q3. What does this experiment prove?

Sound is produced by vibrating bodies.
Vibrations can transfer energy to surrounding media.
Even without contact, energy can move through a medium.

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Case Set 3

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Meena covers a ringing bell inside a jar and removes air using a vacuum pump. The bell still vibrates, but the sound gradually disappears.

Question 1: Q1. Why does the sound disappear in vacuum?

Sound needs a medium (like air) to travel.
Vacuum has no particles to transmit vibrations.
Hence, sound becomes inaudible.

Question 2: Q2. What does this experiment prove?

Sound cannot travel in vacuum.
A material medium is essential for sound propagation.
Sound is mechanical, not electromagnetic.

Question 3: Q3. Can light travel in vacuum?

Yes, light is electromagnetic and doesn’t need a medium.
That’s why we can see sunlight in space.
Unlike sound, light travels in vacuum.

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Case Set 4

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A doctor uses a stethoscope to listen to a patient's heartbeat. The sound is clearly heard through the rubber tubing connected to the chest piece.

Question 1: Q1. How does sound travel through a stethoscope?

Sound travels through the solid rubber tube by particle vibration.
Rubber particles transmit the sound from chest to ears.
It uses conduction through a solid medium.

Question 2: Q2. Is sound louder through solids or air?

Sound travels faster and more efficiently through solids.
Solids have closely packed particles → faster transmission.
Hence, sound is clearer and louder.

Question 3: Q3. What does this demonstrate about mediums?

Sound travels through all mediums: solid, liquid, and gas.
Speed and clarity vary with medium type.
Solids > liquids > gases in sound speed.

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Case Set 5

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A sound wave travels through air and hits a wall. It reflects back and is heard as an echo. Students try to understand the conditions for hearing an echo.

Question 1: Q1. What is an echo?

An echo is a reflected sound wave heard after the original sound.
It occurs when the sound wave bounces off a surface.
Our ears distinguish it if there's a sufficient delay.

Question 2: Q2. What are the conditions for echo formation?

Minimum distance between source and reflector should be ~17 m.
The reflected sound should reach after 0.1 sec.
Hard surface is needed to reflect sound clearly.

Question 3: Q3. Where do we encounter echoes in real life?

In empty halls, mountains, and large corridors.
Used in sonar and ultrasound imaging.
Also occurs in radar and marine navigation.

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Chapter sections

Chapter 11: Sound | Case Study Questions

Passage

Question 1: Q1. What causes the sound in this case?

Question 2: Q2. Can vibrations be seen or felt?

Question 3: Q3. What is the essential condition for production of sound?

Passage

Question 1: Q1. Why does water splash when tuning fork is dipped?

Question 2: Q2. Why can't we always see the fork vibrating?

Question 3: Q3. What does this experiment prove?

Passage

Question 1: Q1. Why does the sound disappear in vacuum?

Question 2: Q2. What does this experiment prove?

Question 3: Q3. Can light travel in vacuum?

Passage

Question 1: Q1. How does sound travel through a stethoscope?

Question 2: Q2. Is sound louder through solids or air?

Question 3: Q3. What does this demonstrate about mediums?

Passage

Question 1: Q1. What is an echo?

Question 2: Q2. What are the conditions for echo formation?

Question 3: Q3. Where do we encounter echoes in real life?

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