Two sound waves X and Y have the same amplitude but X has twice the frequency of Y. Which statement is correct?

X and Y have equal loudness but X has higher pitch

X is louder and has higher pitch

X is quieter and has higher pitch

X and Y have equal loudness but X has higher pitch

X and Y have equal loudness but Y has higher pitch

Assertion (A): The pitch of a man's voice is higher than that of a woman's voice. Reason (R): The vocal cords of a man are longer and thicker, producing vibrations of lower frequency.

Both A and R are true and R is the correct explanation of A.

Both A and R are true but R is not the correct explanation of A.

A student strikes a tuning fork, brings it near her ear, and hears a faint sound. She then touches the vibrating prong to a wooden table and presses her ear against the table, hearing a noticeably louder sound. Explain why the sound is louder in the second case.

Sound travels better through solids than gases because particles in solids are packed closely, transmitting vibrations more efficiently. The wooden table provides a direct solid path to the ear, reducing energy loss and making the sound louder.

Two astronauts on a spacewalk cannot hear the sound of their tools clanking together, even though the tools are in contact with their suits. However, if they press their helmets together, they can hear sounds. Explain this phenomenon using the principles of sound propagation.

Sound cannot travel through the vacuum of space. Without helmet contact, vibrations from the tools travel through the suit but fail to transmit into the helmet’s interior air because of a vacuum gap or poor solid-air coupling. With helmets touching, a continuous solid medium is formed, allowing vibrations to pass directly into the helmet air and then to the ears.

Two sound waves are produced with the same frequency, but one is noticeably louder than the other. Which wave characteristic differs between them? Sketch a simple diagram to show the two wave patterns.

The amplitude of the louder sound wave is larger. Diagram: two sine waves with same wavelength but different peak heights (one taller, one shorter). Label axes and indicate amplitude.

A person standing 680 m from a cliff fires a gun and hears the echo exactly 4 seconds later. Calculate the speed of sound in air. If the air temperature increases slightly, would the echo return faster or slower? Justify your answer.

Speed of sound = (2 × distance) / time = (2 × 680 m) / 4 s = 340 m/s. With higher temperature, the speed of sound increases, so the echo would return faster (less time).

A metal spoon is struck against a table and then immediately touched to the surface of water in a glass. Ripples are observed on the water surface. Explain this observation and relate it to the production of sound.

The ripples appear because the spoon vibrates upon striking, transferring its vibrations to the water. This demonstrates that sound is produced by vibrating objects.

A research vessel uses SONAR to measure the depth of an ocean trench. It emits an ultrasonic pulse and receives the echo after 4.8 seconds. The speed of sound in seawater is 1520 m/s. Calculate the depth of the trench. Also, explain two reasons why ultrasonic waves are chosen for this purpose rather than audible sound waves.

Depth = 3648 m. Ultrasonic waves are used because they have short wavelengths (less diffraction), travel long distances with less loss, and are inaudible so they do not disturb marine life or interfere with other sounds.

While learning about vocal cords, a student places a hand on his throat while humming. He feels vibrations that stop when he stops humming. He also learns that vocal cords are stretched membranes in the larynx. (1) What causes the sensation of vibrations in the throat? (2) Name the organ where vocal cords are located. (3) How does the vibration of vocal cords produce different sounds like high-pitched or low-pitched notes?

(i) Vibration of vocal cords. (ii) Larynx (voice box). (iii) Vocal cords tension is adjusted; higher tension gives higher frequency and pitch, lower tension gives lower pitch.

Class 9 Science Chapter 10: Sound Waves – Characteristics and Applications — Important Questions & Sample Paper

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Understanding sound is fundamental to physics and everyday life. Chapter 10 of CBSE Class 9 Science, “Sound Waves – Characteristics and Applications,” explores the nature of sound as a mechanical wave. It begins with how sound is produced by vibrating bodies, and then delves into the essential requirement of a medium (solid, liquid, or gas) for its propagation. You will investigate what happens to sound in a vacuum through the classic bell jar experiment. The chapter then introduces the key characteristics of a sound wave: wavelength, frequency, time period, amplitude, and pitch. You’ll learn how the ear detects sound and why we can distinguish between a whisper and a shout. Reflection of sound is another major theme, leading to concepts like echo and reverberation, with practical calculations of distance and speed. Applications such as SONAR and the design of concert halls are covered. Common exam questions often include numerical problems on echo, interpreting graphs of sound waves, explaining experiments on sound propagation, and describing the working of SONAR or the human ear. This question bank is designed to help you master these topics with confidence.

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Science — Sound Waves – Characteristics and Applications

Class 9Time: 3 hrsMax Marks: 80

SECTION A

1.
A sound wave has a wavelength of 1.5 m and a frequency of 220 Hz. In which of the following media is it most likely travelling? (Assume speeds: steel ~5000 m/s, water ~1500 m/s, air ~330 m/s, vacuum 0 m/s)
(a) Steel(b) Water(c) Air(d) Vacuum
1
2.
Two sound waves X and Y have the same amplitude but X has twice the frequency of Y. Which statement is correct?
(a) X is louder and has higher pitch(b) X is quieter and has higher pitch(c) X and Y have equal loudness but X has higher pitch(d) X and Y have equal loudness but Y has higher pitch
1
3.
A tuning fork produces sound when its prongs are:
(a) Heated(b) Struck(c) Cooled(d) Bent
1

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In a CBSE exam, this chapter typically contributes questions across the following types. The last column shows how many original questions of each type we have ready in our bank for this chapter:

Question type	Marks each	In our bank
Multiple Choice (MCQ)	1 mark	13
Assertion–Reason	1 mark	6
Short Answer	2 marks	8
Short Answer	3 marks	6
Long Answer	5 marks	5
Case Study	4 marks	6

44 original, exam-style questions in our bank for this chapter — with answers.

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Q1. A sound wave has a wavelength of 1.5 m and a frequency of 220 Hz. In which of the following media is it most likely travelling? (Assume speeds: steel ~5000 m/s, water ~1500 m/s, air ~330 m/s, vacuum 0 m/s)
1 mark
Multiple Choice (MCQ)
(A) Steel(B) Water(C) Air(D) Vacuum
▸ Answer▾ Answer
Air
Q2. Two sound waves X and Y have the same amplitude but X has twice the frequency of Y. Which statement is correct?
1 mark
Multiple Choice (MCQ)
(A) X is louder and has higher pitch(B) X is quieter and has higher pitch(C) X and Y have equal loudness but X has higher pitch(D) X and Y have equal loudness but Y has higher pitch
▸ Answer▾ Answer
X and Y have equal loudness but X has higher pitch
Q3. A tuning fork produces sound when its prongs are:
1 mark
Multiple Choice (MCQ)
(A) Heated(B) Struck(C) Cooled(D) Bent
▸ Answer▾ Answer
Struck
Q4. A sound wave has a time period of 0.00004 s. Which of the following animals can hear this sound? (Hearing ranges: Human: 20–20000 Hz, Dog: 15–50000 Hz, Bat: 1000–120000 Hz)
1 mark
Multiple Choice (MCQ)
(A) Human only(B) Dog only(C) Bat only(D) Both dog and bat
▸ Answer▾ Answer
Both dog and bat
Q5. Assertion (A): The pitch of a man's voice is higher than that of a woman's voice. Reason (R): The vocal cords of a man are longer and thicker, producing vibrations of lower frequency.
1 mark
Assertion–Reason
(A) Both A and R are true and R is the correct explanation of A.(B) Both A and R are true but R is not the correct explanation of A.(C) A is true but R is false.(D) A is false but R is true.
▸ Answer▾ Answer
A is false but R is true.
Q6. A student strikes a tuning fork, brings it near her ear, and hears a faint sound. She then touches the vibrating prong to a wooden table and presses her ear against the table, hearing a noticeably louder sound. Explain why the sound is louder in the second case.
2 marks
Short Answer
▸ Answer▾ Answer
Sound travels better through solids than gases because particles in solids are packed closely, transmitting vibrations more efficiently. The wooden table provides a direct solid path to the ear, reducing energy loss and making the sound louder.
Q7. Two astronauts on a spacewalk cannot hear the sound of their tools clanking together, even though the tools are in contact with their suits. However, if they press their helmets together, they can hear sounds. Explain this phenomenon using the principles of sound propagation.
2 marks
Short Answer
▸ Answer▾ Answer
Sound cannot travel through the vacuum of space. Without helmet contact, vibrations from the tools travel through the suit but fail to transmit into the helmet’s interior air because of a vacuum gap or poor solid-air coupling. With helmets touching, a continuous solid medium is formed, allowing vibrations to pass directly into the helmet air and then to the ears.
Q8. Two sound waves are produced with the same frequency, but one is noticeably louder than the other. Which wave characteristic differs between them? Sketch a simple diagram to show the two wave patterns.
3 marks
Short Answer
▸ Answer▾ Answer
The amplitude of the louder sound wave is larger. Diagram: two sine waves with same wavelength but different peak heights (one taller, one shorter). Label axes and indicate amplitude.
Q9. A person standing 680 m from a cliff fires a gun and hears the echo exactly 4 seconds later. Calculate the speed of sound in air. If the air temperature increases slightly, would the echo return faster or slower? Justify your answer.
3 marks
Short Answer
▸ Answer▾ Answer
Speed of sound = (2 × distance) / time = (2 × 680 m) / 4 s = 340 m/s. With higher temperature, the speed of sound increases, so the echo would return faster (less time).
Q10. A metal spoon is struck against a table and then immediately touched to the surface of water in a glass. Ripples are observed on the water surface. Explain this observation and relate it to the production of sound.
5 marks
Long Answer
▸ Answer▾ Answer
The ripples appear because the spoon vibrates upon striking, transferring its vibrations to the water. This demonstrates that sound is produced by vibrating objects.
Q11. A research vessel uses SONAR to measure the depth of an ocean trench. It emits an ultrasonic pulse and receives the echo after 4.8 seconds. The speed of sound in seawater is 1520 m/s. Calculate the depth of the trench. Also, explain two reasons why ultrasonic waves are chosen for this purpose rather than audible sound waves.
5 marks
Long Answer
▸ Answer▾ Answer
Depth = 3648 m. Ultrasonic waves are used because they have short wavelengths (less diffraction), travel long distances with less loss, and are inaudible so they do not disturb marine life or interfere with other sounds.
Q12. While learning about vocal cords, a student places a hand on his throat while humming. He feels vibrations that stop when he stops humming. He also learns that vocal cords are stretched membranes in the larynx.
4 marks
Case Study
1. (i) What causes the sensation of vibrations in the throat?1 mark
2. (ii) Name the organ where vocal cords are located.1 mark
3. (iii) How does the vibration of vocal cords produce different sounds like high-pitched or low-pitched notes?2 marks
▸ Answer▾ Answer
(i) Vibration of vocal cords. (ii) Larynx (voice box). (iii) Vocal cords tension is adjusted; higher tension gives higher frequency and pitch, lower tension gives lower pitch.

Frequently asked questions

Why does the sound of a ringing bell become inaudible when air is removed from the jar?

Sound is a mechanical wave that requires a material medium to propagate. In the bell jar experiment, as air is pumped out, the density of the medium decreases, so sound waves cannot travel. When almost all air is removed, the vacuum prevents sound transmission, making the bell inaudible even though the hammer still hits it. This proves sound cannot travel through vacuum.

How does SONAR work and why are ultrasonic waves used?

SONAR (Sound Navigation and Ranging) uses the reflection of sound. A transmitter emits ultrasonic waves which travel through water, reflect off the seabed or an object, and the echo is detected by a receiver. The time taken helps calculate distance using the formula d = (v × t)/2. Ultrasonic waves are used because they have high frequency and short wavelength, so they travel in straight lines without bending, and are not absorbed much by water, allowing detection of small objects. Also, they are inaudible to humans.

What is the minimum time gap required to hear a distinct echo? Calculate the minimum distance for an echo if the speed of sound is 340 m/s.

To perceive an echo as a separate sound, the reflected sound must reach the ear at least 0.1 seconds after the original sound. This is due to the persistence of hearing. The minimum distance is d = (speed × time)/2 = (340 × 0.1)/2 = 17 m. So, a reflecting surface must be at least 17 m away for a distinct echo.

Explain why the sound of a tuning fork becomes louder when its stem is placed on a table.

When a tuning fork is struck, its prongs vibrate, producing a weak sound due to small surface area in contact with air. When the stem is pressed against a table, the vibration is forced onto the table's larger surface, which sets a larger volume of air into vibration, increasing the amplitude and making the sound louder. This also shows that sound travels better through solids.

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