Kerala Syllabus Class 9 Physics Chapter 8 Sound Notes Solutions

The comprehensive approach in Kerala Syllabus 9th Standard Physics Textbook Solutions Chapter 8 Sound Notes Questions and Answers English Medium ensures conceptual clarity.

Std 9 Physics Chapter 8 Notes Solutions Sound

SCERT Class 9 Physics Chapter 8 Notes Solutions Kerala Syllabus Sound Questions and Answers

Class 9 Physics Chapter 8 Let Us Assess Answers Sound

Question 1.
Which part of the following sound sources vibrates prominently when sound is produced?
a) Drums
b) Madhalam
c) Bugle
Answer:
Drums – Diaphragm (Stretched membrane)
Madhalam – Diaphragm (Stretched membrane)
Bugle – Air column

Question 2.
A source of sound is an essential component for hearing sound. Which are the other two components?
Answer:
Medium, ear

Question 3.
Plan an activity to demonstrate that sound travels through solids.
Answer:
Meter scale experiment.

Materials required

• Metal meter stick or wooden ruler
• Tuning fork

Procedure

• Meter stick is held horizontally, resting one end on a desk and letting the other end project outside the table.
• Strike the tuning fork to produce sound. Place one end of the tuning fork against the meter stick.
• Have another participant place their ear against the free end of the meter stick.
• They should hear a loud, clear sound through the meter stick.

Question 4.
Write down whether the following statements are true or false. Correct them if wrong.
a) Sound can travel through vacuum.
b) Sound is produced by the vibration of objects.
c) The speed of sound in solids is greater than that in gases.
d) Speed of sound decreases as temperature increases.
Answer:
a) False
Sound can’t travel through vacuum. Because sound requires a medium for its propagation.
b) True
c) True
d) False. Speed of sound increases as temperature increases.

Question 5.
Which of the given musical instruments produce sound by the vibration of the leather diaphragm.
(violin, chenda, flute, mridangam, veena, tabla )
Answer:
Chenda, mridangam, tabla

Question 6.
Can the astronauts directly hear each other while talking on the lunar surface? Why?
Answer:
No. There is no atmosphere on the moon. Sound requires a medium for its propagation.

Question 7.
Write down an example of music and noise
Answer:
Music – sound produced by musical instruments such as guitar, veena, violin etc. Noise – Sound from heavy trucks, railway engine horns, and faulty loudspeakers.

Question 8.
Suggest two ways to reduce sound pollution
Answer:

• Planting more trees around public places
• Avoid traffic jams
• Use less horns while driving

Question 9.
Which of the following mediums has the highest speed of sound? Which has the lowest?
a) Solid
b) Gas
c) Vacuum
d) Liquid
Answer:
Highest speed in (a) solid and lowest speed in (b) gas.

Question 10.
Describe the bell jar experiment to prove that sound requires a medium for propagation.
Answer:
The bell jar experiment demonstrates that sound needs a material medium to travel.

Connect an electric bell to an airtight glass bell jar that’s connected to a vacuum pump.
Suspend the bell inside the jar.
Press the bell’s switch and listen to the bell ring.
Gradually pump out the air from the jar using the vacuum pump. As the air is pumped out, the sound of the bell will become fainter and eventually stop
When there is no air left in the jar, no sound can be heard, even though the bell’s hammer is still vibrating.

Class 9 Physics Chapter 8 Extended Activities Answers Sound

Question 1.
If you have learned instrumental music, play the instrument in the class and explain how it works.
Answer:
Hints
Flute:
Vibration of air column. A flute produces sound when a player blows air into the instrument, which causes the air inside to vibrate and create sound.

Violin:
Vibration of the string produces sound in violin.

A violin produces sound when the player draws a bow across its strings or plucks them. The strings vibrate, and these vibrations transfer to the wooden body of the violin,

Question 2.
Make different types of toys that produce sound and organise a demonstration in the class.
Answer:
Rattle. Materials:

• Small container (like a plastic bottle or tin can)
• Grains (rice, pulses or pebbles)
• Decorative items (paper, cloth)

Steps:

• Fill the container with grains or pebbles
• Seal it securely (use tape or a lid)
• Decorate the outside with coloured paper or cloth
• Shake it to produce sound

Drum Materials:

• Empty tin can or plastic container
• Balloon or thick paper for the drumhead
• Rubber bands or tape

Steps:

• Cut the balloon or paper into a circle that fits over the opening for the can.
• Stretch it over the top and secure it with rubber bands or tape.
• Use your hands or a stick to strike the drum.

Question 3.
Make toy telephone using paper cups and strings and operate them.
Answer:
Material Needed:

• 2 paper cups (or plastic cups)
• String (10-20 feet long)
• Sharp object (pencil or scissors)
• Tape

Steps:

• Prepare a small hole in the bottom of each cup
• Cut the required length of string
• Thread one end of the string through the hole in one cup, tie a knot, and secure with tape if needed. Repeat with the second cup.
• Hold the cups apart, keeping the string tight.
• One person speaks in their cup while the other listens at the other cup.
  

Question 4.
Prepare posters to make people aware of the dangerous of noise pollution.
Answer:

Sound Class 9 Notes Questions and Answers Kerala Syllabus

Question 1.
What are the sounds familiar to you? Write them down.
Answer:

• The ringing sound of the school bell
• The song of cuckoos
• The rolling sound of thunder
• The ringing sound of the school bell
• The song of cuckoos.
• The rolling sound of thunder
• Sound of the horn of vehicles
• Sound of waterfalls
• Sound of different machines
• Sounds from movies
• Sounds of musical instruments

Question 2.
List the situations where sound is useful in daily life.
Answer:
To enjoy music
Answer:

• To enjoy music
• For communication
• Sounds of ambulance and fire engine siren to avoid traffic on road
• Alarm and siren sounds to indicate time
• School bell sound to remind school timings Sounds of vehicle horns for alertness
• Ringtone sounds to indicate phone calls

Activity

Question 3.
Do you hear the sound?
Answer:
Yes

Question 4.
Do you feel the rubber band move back and forth rapidly?
Answer:
Yes

Question 5.
What kind of motion is the rubber band in? (vibration/linear motion)
Answer:
vibration
We are familiar with toys that make sound.

Question 6.
Which are they? Write them down.
Answer:
Olapeeppi, paper whistle, rattle, squeezers, Chiratta veena

Question 7.
Make your favourite toy and listen to its sound. Discuss how it produces sound and write in your science diary.
Answer:
Toy Drum
Use a plastic or paper container as the base, stretch a piece of balloon tightly over the top to create a diaphragm like structure of a drum and secure it with a rubber band. Now a toy drum is ready. Toy drum produces sound by vibration of its diaphragm.

Activity
Excite one prong of a tuning fork by striking it with a rubber hammer. Bring the excited tuning fork close to the ear.

Question 8.
Can you hear the sound?
Answer:
Yes

Gently touch the prongs of the tuning fork. We can feel the vibration in the prongs of the tuning fork.
Excite the tuning fork and touch the prongs gently on the surface of the water in the bowl as shown in figure.
The vibration of the tuning fork causes the splashing of water.

Question 9.
Excite the tuning fork again and hold both its prongs firmly with your hands. Can you hear the sound? Is the tuning fork vibrating now?
Answer:
No. We cannot hear the sound.
The tuning fork is not vibrating now.
We cannot hear the sound because vibration has stopped as we hold both the prongs of tuning fork firmly with our hands.
Inference
Vibration of objects causes the production of sound

Question 10.
What may be the reason for sound from this bell?

Answer:
It is due to the vibration of the metal part of the bell.

Question 11.
Write down examples of sound sources.
Answer:

• Tuning fork
• Musical instruments
• Loudspeaker
• Radio
• Horn of vehicles

You may have noticed the parts that vibrate while playing musical instruments.

Question 12.
List the names of the musical instruments you are familiar with, in the science diary.
Flute
Mridangam
Answer:

• Flute
• Mridangam
• Tabla
• Violin
• Guitar

Question 13.
Which are the vibrating parts of the musical instruments you have listed?
Answer:

Musical instrument	Vibrating part
Flute	Air column
Mridangam	Diaphragm (Stretched membrane)
Tabla	Diaphragm (Stretched membrane)
Violin	Strings
Guitar	Strings

Question 14.
Complete the table by writing the results of your observation.
Answer:

Question 15.
Are the vocal cords the only part that vibrates when we speak? List the associated parts that are likely to vibrate.
The muscles
Answer:
No. It’s not only the vocal cords that vibrate. The associated vibrating parts are

• The muscles
• Throat
• Lips
• Mouth

Question 16.
Which is the main part that vibrates when the following musical instruments are played?
a) Mridangam
b) Flute
c) Guitar
Answer:
a) Mridangam – Diaphragm
b) Flute – Air column
c) Guitar – Strings

Question 17.
List the names of musical instruments in which the air column vibrates as the main or associated part.
Answer:
Flute, Harmonium, Clarinet, Piano, Violin, Veena, Guitar, Chenda, Tabla, drums

Question 18.
Which body part of the organisms listed in the table mainly vibrates when they make sound? Complete the list by gathering information.
Answer:

Creature	Part that vibrates to produce sound
Honeybee	The wings
Elephant	The vocal cords
Mosquito	The wings
Cicada (Cheeveedu)	The wings
Cuckoo	The vocal cords

Question 19.
Can you hear the sound?
Answer:
Yes

Question 20.
Draw the air inside the container into the mouth through the tube attached to the container. Do you sense the sound diminishing?

Answer:
Yes

Question 21.
Try removing some more air. Doesn’t the sound decrease again?
Answer:
Yes

Question 22.
Could you have heard the sound if the air had been completely removed?
Answer:
No. We cannot hear the sound if the air has been completely removed

Question 23.
What can be inferred from this experiment? Write it down in the science diary.
Answer:
Sound keeps on diminishing each time the amount of air inside the container decreases. When the air is completely removed, no sound is heard.

Activity
Let the children place their ears on the desk. Ask another child to excite the tuning fork and press firmly its stem on the desk.

Question 24.
Can you hear the sound?
Answer:
Yes

Question 25.
In this situation, which are the mediums through which sound is transmitted?
Answer:
Desk, air

Question 26.
Can sound travel through solids? Record the inference in the science diary.
Answer:
Yes. Here, the sound travels through the desk, showing that sound travels through solids. Sound can also travel through solids.

Activity
Take water in a bucket. Immerse a steel bowl in the water and tap it with a spoon.

Question 27.
Can you hear the sound?
Answer:
Yes

Question 28.
Through which mediums did sound travel in this case?
Answer:
Water, air

Question 29.
What is the inference from this activity? Write it down in the science diary.
Answer:
Sound travels through water and air and reaches our ears.

Question 30.
Why do astronauts use a radio system to talk to each other?
Answer:
There is no medium in space for communication. Sound cannot travel through vacuum. So they use radio devices.

Question 31.
Does sound travel at the same speed through all mediums?
Answer:
No. The speed of sound is different in different mediums.

Question 32.
In which state of matter is the speed of sound greater? In which is it lesser?
Answer:

Question 33.
At night, the sound of a firecracker is heard 3 s after seeing the flash of light. How far did the explosion take place? (Consider the speed of sound as 350 m/s).
Answer:
The speed of light in air (3 × 10⁸ m/s) is very high. But the speed of sound in the air is only 350 m/s. So, at the time when the firecracker bursts, its light is seen instantly by a person standing far away.
Distance travelled by sound = speed of sound × time = 350 m/s × 3s = 1050 m

Question 34.
In many cases, thunder is heard only a short time after the flash of lightning is seen. Explain the reason?
Answer:
The speed of light in air is 3 × 10⁸ m/s, which is much more than the speed of sound (350 m/s). So thunder is heard only a short time after the flash of lightning is seen.

Question 35.
Don’t you see the mustard seeds moving up and down? Wasn’t the movement of the mustard seeds due to the vibration of the diaphragm?
Answer:
Yes. We can see the mustard seeds moving up and down.
Yes. The movement of the mustard seeds was due to the vibration of the diaphragm.

Question 36.
Discuss the challenges faced by hearing impaired and write it in your science diary.
A barrier to communications
Prone to accident
Answer:

• A barrier to communications
• Prone to accident
• Safety issues
• Employment barriers

Question 37.
What should be the approach to the hearing impaired? Discuss based on the indicators.
Be empathetic
Give consideration and include them in all activities
Answer:

• Be empathetic
• Give consideration and include them in all activities
• Respect their needs
• Encourage participation

Question 38.
Based on this, prepare a short note to present on world hearing day.
Answer:
Title: Understanding and supporting the hearing impaired 3^rd march is world hearing day, which reminds us how important hearing health is and the challenges faced by those with hearing loss. It is essential to know how we can help them. They face many challenges in communication, education, travelling, employment etc. We can help them by effective approaches.

They are,
Speak clearly: Talk at a normal speed and face the person you are speaking to. Minimize background noise: Keep the environment quite so it is easier to hear. Be patient: Give them time to respond and be ready to repeat things if needed.
On World Hearing Day, let’s promise to raise awareness about hearing health and use inclusive communication. By understanding and supporting each other, we can help make sure everyone feels heard and included.

Beethoven gifted the world with the most melodious music. Helen Keller proved that it is possible to achieve great success in life with self-confidence, determination and hard work without flinching in adverse life situations. Many such great people have overcome hearing disorders and outshone in life.

Hearing loss can be detected through hearing tests using an audiometer.

A hearing aid is an electronic device that helps individuals with hearing loss to hear more clearly.

Question 39.
Conduct an interview with an audiologist about the hearing test and share the information with your classmates.
Answer:
This is an example of data collected from an audiologist.
Hearing Test Process:

• Starts with a medical history.
• Main test: Pure tone audiometry (listening to sounds through headphones).

Test Details:

• Conducted in a soundproof booth.
• Measures different frequencies and volumes; results are shown on an audiogram.

Age-Specific Testing:

• Children: Use play-based tests.
• Adults: May include speech understanding tests.

Common Hearing Issues:

• Age-related hearing loss.
• Noise-induced hearing loss.
• Conductive hearing loss (from infections).

Preparing for a Hearing Test:

• Rest well before the test.
• Avoid loud noises beforehand.
• Bring any medical records and symptom notes.

Advice for Suspected Hearing Loss:

• Seek help early if you have hearing difficulties.
• Early intervention is important.

Question 40.
Find out the key aspects related to ear care that we should pay attention to and present them in the class.
Answer:
1. Regular cleaning
Avoid cotton buds: They can push wax deeper.
Use a damp cloth: clean only the outer ear.

2. Prevent water damage
Dry ears after swimming: Use a towel or tilt your ear. Wear earplugs: Use them while swimming.

3. Healthy lifestyle
Balanced diet: Nutrients like vitamins are good for ear health.
Stay hydrated: Helps maintain ear moisture.

4. Stay away from extremely loud noises, and while using headphones, stick to a volume range that is said to be safe.

Question 41.
Compare the pleasing music you hear in music class with the noise at the traffic point. Which sound is pleasant to hear?
Answer:
Music from music class.

Question 42.
You can listen to enchanting music from Chirattaveena. Then, listen to the sound of a coconut shell (Chiratta) being rubbed against a stone. Compare the sound in both cases.
Answer:
The sound from a chirattaveena is pleasing to hear and that from a chiratta rubbed on a stone is not
pleasant to hear.

There are certain times in which music feels like noise. Also, sound beyond a certain limit seems to be annoying.

Question 43.
What is your response to this statement?
Answer:
Noise pollution is harmful to every living being. It can cause severe health issues.

Question 44.
What can be the cause of noise pollution?
Answer:

• Increasing number of vehicles
• Public address systems
• Noise from construction sites
  

Noise affects not only our physical health but also our mental health and emotional health.

Question 45.
Find out more about this from health care professionals and record them in the science diary.
Answer:
Physical Health:

• Hearing Loss: Prolonged exposure can damage hearing.
• Cardiovascular Issues: Linked to hypertension and heart disease due to stress.
• Sleep Disturbances: Noise disrupts sleep, leading to fatigue.

Mental Health:

• Increases Stress and Anxiety
• Affects concentration and memory, especially in children.
• Depression: Contributes to feelings of isolation and helplessness.

Emotional Health:

• Noise can lead to irritability and affect relationships.
• Reduces overall life satisfaction.
• May lead to unhealthy coping strategies

Question 46.
Which professional groups are most affected by noise pollution
Answer:
Health care workers, teachers, musicians.