This MCQ module is based on: Sound Waves: Characteristics and Applications — NCERT Exercises
TOPIC 38 OF 50
Sound Waves: Characteristics and Applications — NCERT Exercises
🎓 Class 9
Science
CBSE
Theory
Ch 10 — Sound Waves: Characteristics and Applications
⏱ ~15 min
🌐 Language: [gtranslate]
🧠 AI-Powered MCQ Assessment
▲
📝 Worksheet / Assessment
▲
This assessment will be based on: Sound Waves: Characteristics and Applications — NCERT Exercises
Upload images, PDFs, or Word documents to include their content in assessment generation.
Chapter 10 — Sound: Quick Summary
This chapter explored how sound is born, how it travels, what makes it loud or shrill, and how its reflection gives us echoes, SONAR and the warmth of music in a hall. Below is a compact recap.
Source
All sounds come from a vibrating object — vocal cords, tuning fork, drum, guitar string.
Medium
Sound needs a material medium. It cannot travel through a vacuum (bell-jar experiment).
Wave type
Sound is a longitudinal wave — particles oscillate parallel to direction of travel, producing compressions and rarefactions.
Speed order
v(solid) > v(liquid) > v(gas). In air at 20 °C, v ≈ 343 m/s.
Wave equation
v = λν and T = 1/ν.
Pitch
Decided by frequency. High ν → high pitch.
Loudness
Decided by amplitude. Energy ∝ A². Measured in decibel (dB).
Quality / Timbre
Decided by wave shape; lets us distinguish two sources playing the same note.
Hearing range
Audible: 20 Hz – 20 000 Hz. Below = infrasonic. Above = ultrasonic.
Echo
Distinct repetition; needs ≥ 0.1 s gap → distance ≥ 17.2 m at v = 344 m/s.
Reverberation
Persistence of sound by repeated reflections in a hall; controlled by absorbent surfaces.
SONAR
Sound Navigation And Ranging — ultrasound + echo to map seabed and detect submarines. d = vt/2.
Human ear
Outer (pinna, canal, eardrum) → Middle (hammer–anvil–stirrup ossicles) → Inner (cochlea, auditory nerve).
Ultrasound uses
Echocardiography, sonography, breaking kidney stones, cleaning fine parts, crack detection, SONAR.
Key Terms
VibrationRapid to-and-fro motion of an object about its mean position.
CompressionRegion of high density and pressure in a longitudinal wave.
RarefactionRegion of low density and pressure in a longitudinal wave.
Wavelength (λ)Distance between two consecutive compressions or rarefactions.
Frequency (ν)Number of complete oscillations per second; SI unit hertz (Hz).
Time period (T)Time taken for one complete oscillation; T = 1/ν.
Amplitude (A)Maximum displacement of a particle from its rest position.
PitchPerceived shrillness; depends on frequency.
LoudnessPerceived strength of sound; depends on amplitude.
Quality / TimbreProperty that distinguishes two sounds of same pitch and loudness.
Audible range20 Hz to 20 000 Hz.
Infrasonic / UltrasonicSounds below 20 Hz / above 20 000 Hz; inaudible to humans.
EchoDistinct reflected sound heard after the original.
ReverberationPersistence of sound in a hall by repeated reflections.
SONARSound Navigation And Ranging — depth/object detection by ultrasound echoes.
CochleaSpiral, fluid-filled organ of inner ear that converts vibrations to nerve signals.
NCERT Exercises — Step-by-Step Solutions
1How does sound travel from one place to another? L2
Solution. Sound is produced by a vibrating object. The vibrating body forces the surrounding particles of the medium to oscillate. These particles bunch together (compression) and spread apart (rarefaction) repeatedly, passing the disturbance to the next layer of particles. The energy thus moves from one point to another as a longitudinal wave, even though the particles themselves only oscillate about their mean positions.
2Explain how sound is produced by your school bell. L2
Solution. When the school bell is struck by a hammer, the metal of the bell starts vibrating rapidly. These mechanical vibrations push and pull on the surrounding air, creating alternate compressions and rarefactions that travel outward as sound waves. If you touch the bell immediately after striking it, you can feel the vibration that produced the sound.
3Why are sound waves called mechanical waves? L2
Solution. Sound waves cannot propagate without a material medium — they need particles of solid, liquid or gas to transfer the vibration onward. Such waves that depend on the mechanical motion of particles of the medium are called mechanical waves. Light, on the other hand, can travel even through vacuum and is therefore not a mechanical wave.
4Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend? L3
Solution. No. The Moon has practically no atmosphere; there are almost no air molecules to set into vibration. Without a medium to carry the compressions and rarefactions, sound cannot travel from your friend's mouth to your ear. Astronauts on the Moon talk to one another through radios, because radio waves are electromagnetic and do not need a medium.
5Which wave property determines (a) loudness, (b) pitch? L1
Solution. (a) Loudness is determined by the amplitude of the wave (in fact, energy carried is proportional to A²). (b) Pitch is determined by the frequency; a higher frequency gives a higher (shriller) pitch.
6Guess which sound has a higher pitch: guitar or car horn? L2
Solution. The guitar has a higher pitch. Its strings vibrate at much higher frequencies (typically a few hundred to over a thousand hertz) than the deep, low-frequency horn of a car (around 200 Hz or less). Higher frequency = higher pitch.
7What are wavelength, frequency, time period and amplitude of a sound wave? L1
Solution.
- Wavelength (λ): distance between two consecutive compressions or two consecutive rarefactions. SI unit: m.
- Frequency (ν): number of complete oscillations made per second. SI unit: hertz (Hz).
- Time period (T): time taken to complete one full oscillation. T = 1/ν. SI unit: second.
- Amplitude (A): maximum displacement of a particle of the medium from its rest position when the wave passes.
8How are wavelength and frequency of a sound wave related to its speed? L2
Solution. The speed v, wavelength λ and frequency ν of a sound wave are linked by the relation
\(v = \lambda \times \nu\)
For a given medium and temperature, v is constant. So if frequency increases, wavelength decreases proportionally and vice versa.
9Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium. L3
Given: ν = 220 Hz, v = 440 m/s.
To find: λ.
Using v = λν:
To find: λ.
Using v = λν:
\(\lambda = \dfrac{v}{\nu} = \dfrac{440}{220} = 2 \text{ m}\)
Answer: wavelength = 2 m.
10A person clapping his hands sends two claps per second. The sound travels at 340 m/s. What is the distance between successive compressions? L3
Given: ν = 2 Hz, v = 340 m/s.
Distance between two successive compressions = wavelength λ.
Distance between two successive compressions = wavelength λ.
\(\lambda = \dfrac{v}{\nu} = \dfrac{340}{2} = 170 \text{ m}\)
Answer: 170 m.
11Distinguish between loudness and intensity of sound. L2
Solution.
- Intensity is a physical quantity — the sound energy passing per second through unit area held perpendicular to the direction of the wave. It is measurable and does not depend on the listener.
- Loudness is a subjective sensation of the strength of sound felt by the listener. It depends on the intensity but also on the sensitivity of the ear and the frequency of the sound. Two listeners may judge the loudness of the same sound differently.
12In which medium — air, water or iron — does sound travel fastest at a given temperature? L1
Solution. Sound travels fastest in iron (a solid). Order of speeds: v(iron) > v(water) > v(air). The reason is that the particles of a solid are tightly bound and pass on vibrations rapidly, while the loosely-spaced gas molecules of air transfer them slowly.
13An echo is heard in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 m/s? L3
Given: t = 3 s, v = 342 m/s.
Total distance covered by sound (to the surface and back) = v × t = 342 × 3 = 1026 m.
Distance from source to reflecting surface = total distance / 2:
Total distance covered by sound (to the surface and back) = v × t = 342 × 3 = 1026 m.
Distance from source to reflecting surface = total distance / 2:
\(d = \dfrac{v \times t}{2} = \dfrac{1026}{2} = 513 \text{ m}\)
Answer: 513 m.
14Why are the ceilings of concert halls curved? L4
Solution. Concert hall ceilings are curved (often concave) so that the sound from the stage, after reflection from the ceiling, spreads evenly to every part of the audience. The shape acts like a sound reflector — it reduces dead spots near the back, equalises loudness across the hall and helps keep the music clear without electronic amplification.
15A submarine emits a SONAR pulse, which returns from an underwater cliff in 1.02 s. If the speed of sound in salt water is 1531 m/s, how far away is the cliff? L3
Given: t = 1.02 s, v = 1531 m/s.
Total distance travelled by the pulse = v × t = 1531 × 1.02 = 1561.62 m.
The pulse goes to the cliff and back, so:
Total distance travelled by the pulse = v × t = 1531 × 1.02 = 1561.62 m.
The pulse goes to the cliff and back, so:
\(d = \dfrac{v \times t}{2} = \dfrac{1561.62}{2} ≈ 780.81 \text{ m}\)
Answer: The cliff is about 780.8 m away from the submarine.
End of Chapter 10. Revise this part along with Parts 1–3 before attempting board-style questions. Practise the v = λν and d = vt/2 numericals till they feel automatic.
Frequently Asked Questions — NCERT Exercises & Intext Questions
How do I solve NCERT Class 9 Science Chapter 10 (Sound Waves: Characteristics and Applications) exercise questions for the CBSE board exam?
Solve NCERT Chapter 10 — Sound Waves: Characteristics and Applications — exercise questions by first reading the question carefully, writing down the given data, recalling the relevant concepts like sound, longitudinal wave, frequency, and applying them step by step. This Part 4 covers every intext and end-of-chapter exercise from the NCERT textbook. Write balanced equations, label diagrams clearly and show each step — CBSE Class 9 examiners award step marks even if the final answer has a small slip. Practising these solutions strengthens conceptual clarity and builds speed for both the school exam and the upcoming Class 10 board exam.
Are the NCERT intext questions from Sound Waves: Characteristics and Applications important for the Class 9 Science exam?
Yes, NCERT intext questions for Chapter 10 Sound Waves: Characteristics and Applications are highly important for the CBSE Class 9 Science exam. Many questions in school and competitive papers are directly lifted or only slightly modified from these intext questions, and they test the foundational concepts — sound, longitudinal wave, frequency — that chapter-end questions and the Class 10 board build on. Attempt every intext question first, then move on to the exercises. This practice ensures complete NCERT coverage, which is the CBSE syllabus's primary source.
What types of questions from Sound Waves: Characteristics and Applications are asked in the Class 9 Science exam?
The Class 9 Science paper (CBSE pattern) asks a mix of question types from Sound Waves: Characteristics and Applications: 1-mark MCQ and assertion-reason, 2-mark short answers, 3-mark explanations, 5-mark long answers with diagrams or derivations, and 4-mark competency-based / case-study questions. These test understanding of sound, longitudinal wave, frequency, wavelength. Practising every NCERT exercise and intext question prepares you to answer all of these formats with confidence.
How many marks does Chapter 10 — Sound Waves: Characteristics and Applications — typically carry in the Class 9 Science paper?
Chapter 10 — Sound Waves: Characteristics and Applications — is part of the CBSE Class 9 Science syllabus and typically contributes 5–9 marks in the annual paper, depending on the year's weightage. Questions are drawn from definitions, reasoning, numerical/descriptive problems and diagrams on topics like sound, longitudinal wave, frequency. Solving the NCERT exercises in this part is essential because CBSE directly references the NCERT Exploration textbook for question design.
Where can I find step-by-step NCERT solutions for Chapter 10 Sound Waves: Characteristics and Applications Class 9 Science?
You can find complete, step-by-step NCERT solutions for Chapter 10 Sound Waves: Characteristics and Applications Class 9 Science on MyAiSchool. Every intext and end-of-chapter exercise question is solved with full working, labelled diagrams and CBSE-aligned mark distribution. Solutions highlight key points about sound, longitudinal wave, frequency that examiners look for. This makes revision quick and exam-focused for Class 9 CBSE students.
What is the best way to revise Sound Waves: Characteristics and Applications for the Class 9 Science exam?
The best way to revise Sound Waves: Characteristics and Applications for the CBSE Class 9 Science exam is a three-pass approach. First pass: skim the chapter and note down key terms like sound, longitudinal wave, frequency in a one-page mind map. Second pass: solve every NCERT intext and exercise question without looking at the solution, then self-check. Third pass: attempt sample papers and competency-based questions under timed conditions. This structured revision secures full marks for this chapter.
AI Tutor
Science Class 9 — Exploration
Ready