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CBSE Class 9 Physics Chapter 11 Sound Worksheet with Answers

Welcome to the CBSE Class 9 Physics Chapter 11 Sound worksheet, designed to help you master one of the most practical and fascinating topics in physics. Sound surrounds us every day — from the alarm clock in the morning to music, speech, traffic noise, and even silence. This worksheet is structured to test your understanding of sound production, propagation, characteristics (pitch, loudness, timbre), reflection, echo, SONAR, and the human ear. Complete all sections within 90 minutes for best results. Print this page and solve it as a mock test to evaluate your readiness for school exams and the CBSE board.

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Key takeaways

  • ✓Sound is a longitudinal wave produced by vibrating objects and requires a medium (solid, liquid, or gas) to propagate; it cannot travel in a vacuum.
  • ✓Speed of sound varies by medium: fastest in solids (~5000 m/s in steel), slower in liquids (~1480 m/s in water), and slowest in gases (~343 m/s in air at 20°C).
  • ✓Pitch depends on frequency (measured in Hertz); loudness depends on amplitude; timbre distinguishes sounds from different sources at the same pitch and loudness.
  • ✓An echo is heard when reflected sound reaches the ear at least 0.1 seconds after the original sound, requiring a minimum distance of 17 meters from the reflecting surface.
  • ✓SONAR (Sound Navigation and Ranging) uses ultrasound reflection to detect underwater objects and measure distances, vital for submarines, fishing, and medical imaging.
  • ✓The human ear converts sound waves into electrical signals through the eardrum, ossicles, and cochlea; humans hear frequencies from 20 Hz to 20,000 Hz.
  • ✓Ultrasound (>20 kHz) and infrasound (<20 Hz) lie outside the human hearing range but have important applications in medicine, navigation, and animal communication.

Quick Chapter Recap: Sound (NCERT Class 9 Physics Chapter 11)

Sound is a form of energy produced by vibrating objects and travels as longitudinal waves through a medium — solid, liquid, or gas. Unlike light, sound cannot travel in vacuum because it needs particles to transmit the disturbance. When an object vibrates, it creates compressions (high-pressure regions where particles bunch together) and rarefactions (low-pressure regions where particles spread apart). The speed of sound is highest in solids because particles are tightly packed and transfer vibrations efficiently. In air at 20°C, sound travels at approximately 343 m/s; in water at 1480 m/s; and in steel at around 5000 m/s. The characteristics of sound are pitch (determined by frequency), loudness (determined by amplitude), and timbre (quality or tone color that helps us distinguish between different sources). Reflection of sound from hard surfaces creates echoes when the reflected sound reaches the ear at least 0.1 seconds after the original. This principle is used in SONAR technology for underwater navigation and in medical ultrasound imaging. The human ear is a sophisticated organ divided into outer, middle, and inner parts, converting sound waves into electrical signals sent to the brain.
  • Sound is a longitudinal wave requiring a medium; it cannot travel in vacuum
  • Speed of sound: solids > liquids > gases (e.g., steel 5000 m/s, water 1480 m/s, air 343 m/s)
  • Pitch ∝ frequency; Loudness ∝ amplitude; Timbre = unique sound quality
  • Echo: distinct reflected sound heard ≥0.1 s after original (minimum distance 17 m)
  • SONAR uses ultrasound reflection for underwater detection and distance measurement
  • Human hearing range: 20 Hz to 20,000 Hz; ultrasound >20 kHz, infrasound <20 Hz

Section A: Multiple Choice Questions (MCQs)

This section contains 8 multiple-choice questions testing your foundational understanding of sound, its properties, propagation, and applications. Each question carries 1 mark. Choose the most appropriate option. These MCQs cover NCERT concepts and are typical of CBSE board exam style. Pay attention to keywords like 'fastest', 'minimum distance', 'frequency', and 'amplitude' — they often hold the key to the correct answer. Remember that sound speed increases with temperature and density of the medium, and that echoes require specific distance criteria. Solve all questions and verify your answers against the answer key at the end. No negative marking, so attempt every question even if you are unsure.
  • Q1. Sound is produced by: (a) stationary objects (b) vibrating objects (c) objects at rest (d) smooth surfaces
  • Q2. Sound waves are: (a) transverse waves (b) longitudinal waves (c) electromagnetic waves (d) none of these
  • Q3. In which medium does sound travel the fastest? (a) Air (b) Water (c) Steel (d) Vacuum
  • Q4. The pitch of sound depends on its: (a) amplitude (b) frequency (c) speed (d) timbre
  • Q5. The minimum distance required to hear an echo is approximately: (a) 10 m (b) 17 m (c) 34 m (d) 50 m
  • Q6. SONAR stands for: (a) Sound Navigation and Rotation (b) Sound Navigation and Ranging (c) Sonic Navigation and Ranging (d) Speed Of Navigation And Ranging
  • Q7. Ultrasound has frequency: (a) less than 20 Hz (b) between 20 Hz and 20 kHz (c) more than 20 kHz (d) exactly 20 Hz
  • Q8. The eardrum is located in the: (a) outer ear (b) middle ear (c) inner ear (d) cochlea

Section B: Fill in the Blanks

Complete the following sentences with the correct term from the chapter. Each blank carries 1 mark. This section tests your recall of key definitions and facts from NCERT Class 9 Physics Chapter 11. Write your answers clearly. Use exact terminology as given in the textbook — for instance, 'longitudinal' not 'compression', 'frequency' not 'vibration rate', and 'cochlea' not 'inner ear organ'. Read each sentence carefully; sometimes a small grammatical clue (like 'a' vs 'an' or singular vs plural) can guide you to the right word. Fill all blanks even if you are uncertain, then cross-check with the answer key provided at the end of this worksheet.
  • Q9. Sound cannot travel through __________ because there are no particles to carry the vibrations.
  • Q10. The regions in a longitudinal wave where particles are closely packed are called __________.
  • Q11. The sensation of sound that depends on amplitude is called __________.
  • Q12. The characteristic that allows us to distinguish between sounds from a piano and a violin is called __________.
  • Q13. The prolonged multiple reflections of sound that blend together are known as __________.
  • Q14. The technology that uses sound reflection to detect underwater objects is __________.
  • Q15. The audible range of frequencies for humans is from __________ Hz to __________ Hz.
  • Q16. The spiral-shaped fluid-filled organ in the inner ear that converts vibrations into electrical signals is the __________.

Section C: True or False (with Correction)

Read each statement carefully and write True or False. If the statement is False, rewrite it correctly in the space provided. Each question carries 1 mark (0.5 for identifying False, 0.5 for correction). This format is common in CBSE worksheets and term exams and tests both your knowledge and your ability to identify misconceptions. Pay close attention to units, direction of particle motion, and the conditions under which phenomena like echo occur. Do not leave any question unattempted. Even if you are unsure, make an educated guess and compare with the answer key later. Understanding why a statement is false is as important as knowing the correct fact — it deepens your conceptual clarity and prevents common exam mistakes.
  • Q17. Sound travels fastest in gases. (True / False)
  • Q18. The pitch of a sound is determined by its amplitude. (True / False)
  • Q19. Echoes are produced only when sound reflects from soft surfaces like curtains. (True / False)
  • Q20. Infrasound has a frequency greater than 20,000 Hz. (True / False)
  • Q21. The ossicles are located in the inner ear. (True / False)
  • Q22. A vibrating tuning fork produces sound by creating compressions and rarefactions in the surrounding medium. (True / False)

Section D: Short Answer Questions (2–3 Marks Each)

Answer the following questions in 30–50 words each. These questions are designed to test your understanding of concepts, definitions, and simple numerical reasoning. Each carries 2 or 3 marks as indicated. Write clearly and use correct scientific terminology from the NCERT textbook. For numerical questions, always write the given data, formula, substitution, and final answer with proper units. Marks are awarded not just for the final answer but also for the method and explanation. If a question asks 'Why?', provide a reason grounded in physics principles — for example, 'because particles in solids are closer together' or 'because reflection requires a time gap of at least 0.1 seconds'. Practice writing concise, point-based answers; avoid long essays. Refer to the answer key to compare your approach and refine your exam writing technique.
  • Q23. [2 marks] Why is sound unable to travel through vacuum? Explain with an example.
  • Q24. [2 marks] Define frequency and state its SI unit. How is frequency related to pitch?
  • Q25. [3 marks] A man shouts near a cliff and hears an echo after 3 seconds. If the speed of sound in air is 340 m/s, calculate the distance of the cliff from the man.
  • Q26. [2 marks] Differentiate between echo and reverberation.
  • Q27. [3 marks] Explain how SONAR works. Mention one practical application.
  • Q28. [2 marks] What is ultrasound? Give two uses of ultrasound.
  • Q29. [2 marks] Name the three parts of the human ear and state the function of the eardrum.

Section E: Long Answer and HOTS Questions (5 Marks Each)

These questions test your ability to integrate multiple concepts, apply critical thinking, and explain phenomena in detail. Each question carries 5 marks. Write your answers in 80–120 words, using diagrams where helpful. Structure your answer in clear points or paragraphs. For numerical HOTS problems, show all steps: given data, formula, substitution, calculation, and conclusion with proper units. Marks are distributed for understanding, method, accuracy, and presentation. These questions often appear in CBSE board exams and require deeper conceptual insight — they go beyond recall and test your analytical skills. Read the question twice, underline key terms, plan your answer mentally, and then write. Compare your responses with the detailed solutions in the answer key to identify gaps and improve your exam technique. These are the questions that distinguish average students from high scorers.
  • Q30. [5 marks] Describe the process of production and propagation of sound in air. Use the terms 'vibration', 'compression', and 'rarefaction' in your answer. Draw a simple diagram of a longitudinal wave.
  • Q31. [5 marks] Explain the three characteristics of sound: pitch, loudness, and timbre. How do they help us distinguish between different sounds? Give one example for each.
  • Q32. [5 marks] A SONAR device on a ship sends a signal and receives an echo after 4 seconds. If the speed of sound in seawater is 1500 m/s, calculate the depth of the seabed. Also explain why SONAR uses ultrasound and not audible sound.

Section F: Case-Study Question (4 Marks)

Read the following case study carefully and answer the questions that follow. This format is increasingly common in CBSE exams and tests your ability to apply concepts to real-world scenarios. The case study typically describes a situation or experiment and is followed by 3–4 sub-questions (MCQ or short-answer). Marks are awarded for comprehension, application, and reasoning. Read the passage twice, underline key data (distances, times, speeds), and refer back to it while answering each sub-question. Even if one sub-question seems difficult, attempt the others — they are often independent. This section bridges theory and practice, showing how physics explains everyday phenomena. Compare your answers with the detailed key at the end to improve your case-study solving skills for board exams.

Complete Answer Key with Explanations

Below is the complete answer key for all sections of this worksheet. Each answer includes a brief explanation or working to help you understand the reasoning. Use this key not just to check your answers, but to learn the correct approach and fill conceptual gaps. If you scored below 70%, revisit the NCERT chapter, revise definitions, and solve the worksheet again after a few days. If you scored above 85%, you are well-prepared for the chapter test. For personalized doubt-solving and step-by-step explanations with photo upload, consider CBSETUTOR.ai — a 24×7 AI tutor for CBSE students at a flat ₹999/month for all classes (6–12), with a 3-day free trial. Now review each answer carefully, mark your mistakes, and note down topics that need more practice.
  • A1. (b) vibrating objects — Sound is always produced by vibration of an object.
  • A2. (b) longitudinal waves — Particle displacement is parallel to wave direction.
  • A3. (c) Steel — Sound travels fastest in solids, slowest in gases.
  • A4. (b) frequency — Higher frequency = higher pitch.
  • A5. (b) 17 m — Minimum distance = (340 m/s × 0.1 s) ÷ 2 = 17 m.
  • A6. (b) Sound Navigation and Ranging — Standard acronym.
  • A7. (c) more than 20 kHz — Ultrasound is above human hearing range.
  • A8. (b) middle ear — The eardrum separates outer and middle ear.
  • A9. vacuum — No particles means no medium for sound propagation.
  • A10. compressions — High-pressure regions in longitudinal wave.
  • A11. loudness — Loudness depends on amplitude of vibration.
  • A12. timbre (or quality) — Allows us to distinguish between different instruments.
  • A13. reverberation — Multiple reflections blend together.
  • A14. SONAR — Sound Navigation and Ranging technology.
  • A15. 20 Hz to 20,000 Hz — Audible range for humans.
  • A16. cochlea — Spiral organ in inner ear containing hair cells.
  • A17. False. Correction: Sound travels fastest in solids, not gases.
  • A18. False. Correction: Pitch is determined by frequency, not amplitude.
  • A19. False. Correction: Echoes are produced when sound reflects from hard, rigid surfaces.
  • A20. False. Correction: Infrasound has frequency less than 20 Hz; ultrasound is >20 kHz.
  • A21. False. Correction: The ossicles (hammer, anvil, stirrup) are in the middle ear.
  • A22. True. — This correctly describes sound production by vibration.
  • A23. Sound requires a medium (solid, liquid, or gas) to propagate because sound waves are mechanical waves that travel by particle vibration. In vacuum, there are no particles to vibrate and transfer the disturbance, so sound cannot travel. Example: Astronauts in space use radios because sound cannot travel in the vacuum of space.
  • A24. Frequency is the number of vibrations or oscillations completed in one second. SI unit: Hertz (Hz). Frequency is directly related to pitch — higher frequency produces higher pitch, and lower frequency produces lower pitch.
  • A25. Given: Time = 3 s, Speed = 340 m/s. Total distance = 340 × 3 = 1020 m. Distance of cliff = 1020 ÷ 2 = 510 m. (Sound travels to cliff and back.)
  • A26. Echo: A distinct repetition of sound heard separately after reflection, occurring when the reflected sound reaches the ear ≥0.1 s after the original. Reverberation: Prolonged, blended sound caused by multiple reflections in a confined space, where echoes overlap and are not heard separately.
  • A27. SONAR sends ultrasound waves into water. When these waves hit an object (like the seabed or a submarine), they reflect back. The device measures the time taken for the echo to return. Using the formula distance = (speed × time) ÷ 2, it calculates the distance to the object. Application: Used by ships to measure ocean depth, detect underwater objects, locate fish schools, or navigate safely.
  • A28. Ultrasound is sound with frequency greater than 20,000 Hz, above the human hearing range. Uses: (i) Medical imaging (ultrasound scans for pregnancy and organs), (ii) Cleaning delicate instruments, detecting cracks in metal structures, and SONAR technology.
  • A29. Three parts: Outer ear (pinna and ear canal), Middle ear (eardrum and ossicles), Inner ear (cochlea). Eardrum function: It is a thin membrane that vibrates when sound waves strike it, transmitting vibrations to the ossicles in the middle ear.
  • A30. Production: Sound is produced when an object vibrates. Vibrations cause disturbances in the surrounding medium. Propagation: These disturbances travel as longitudinal waves. The vibrating object creates compressions (regions where particles are pushed together, high pressure) and rarefactions (regions where particles are spread apart, low pressure). These compressions and rarefactions move forward through the medium, transferring energy from particle to particle without the particles themselves moving forward. Diagram: Draw a series of dots representing air particles, with clusters (compressions) and gaps (rarefactions) moving to the right, labeled accordingly.
  • A31. (i) Pitch: Sensation of sound that depends on frequency. Higher frequency = higher pitch (e.g., a whistle); lower frequency = lower pitch (e.g., a drum). (ii) Loudness: Sensation depending on amplitude. Larger amplitude = louder sound (e.g., a shout vs whisper). (iii) Timbre (Quality): Characteristic that distinguishes sounds of the same pitch and loudness from different sources (e.g., a flute and a guitar playing the same note sound different due to different harmonics). Together, these help us recognize voices, instruments, and environmental sounds.
  • A32. Given: Time = 4 s, Speed in seawater = 1500 m/s. Total distance = 1500 × 4 = 6000 m. Depth of seabed = 6000 ÷ 2 = 3000 m = 3 km. SONAR uses ultrasound because: (i) Ultrasound has short wavelength, so it can be directed in narrow beams for precise detection. (ii) It does not interfere with marine life or human hearing. (iii) Audible sound spreads in all directions and is less accurate for distance measurement.
  • A33. (b) 680 m — Distance = speed × time = 340 × 2 = 680 m (total distance travelled).
  • A34. (b) 340 m — Distance of cliff = 680 ÷ 2 = 340 m (one-way distance).
  • A35. For a distinct echo to be heard, the reflected sound must reach the ear at least 0.1 seconds after the original sound. This requires a minimum distance of about 17 metres. If closer, the brain cannot distinguish the original and reflected sounds separately.
  • A36. Reverberation would occur. The reflected sound would blend with the original, creating a prolonged, muddled sound rather than a distinct echo.

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Tips to Excel in Chapter 11 Sound

To score full marks in Sound, focus on clarity of concepts and consistent practice. First, memorize key definitions verbatim from NCERT — terms like compression, rarefaction, pitch, loudness, timbre, echo, reverberation, SONAR, ultrasound, and infrasound appear frequently in exams. Second, practice numerical problems on echo and SONAR daily; these carry 3–5 marks and have a fixed formula. Always write the given data, formula, substitution, and final answer with units — even if your calculation is slightly off, you will get method marks. Third, draw neat labeled diagrams for the human ear and longitudinal waves; diagrams often fetch you 1–2 extra marks and demonstrate clear understanding. Fourth, understand the difference between similar terms like echo vs reverberation, pitch vs loudness, and ultrasound vs infrasound — these are common sources of confusion and exam errors. Fifth, connect theory to daily life: think about why concert halls have specific wall materials, why you hear echoes in empty rooms, why doctors use ultrasound scans. Real-world connections make concepts stick. Finally, solve previous year CBSE question papers and sample papers; they reveal the exact question style, difficulty level, and marking scheme. If you encounter doubts, do not leave them unresolved — use resources like NCERT Exemplar, reference books, or CBSETUTOR.ai for instant clarification. Consistent revision, active problem-solving, and conceptual clarity are the three pillars of success in physics.
  • Memorize definitions and key terms from NCERT word-for-word
  • Practice echo and SONAR numericals daily; always show full working
  • Draw labeled diagrams for ear structure and longitudinal waves
  • Distinguish carefully between pitch vs loudness, echo vs reverberation, ultrasound vs infrasound
  • Relate concepts to real life (concert halls, medical imaging, animal navigation)
  • Solve previous year CBSE papers to understand question patterns and marking schemes
  • Use CBSETUTOR.ai or other resources to resolve doubts immediately

Frequently asked questions

What is the minimum distance required to hear a clear echo?+
The minimum distance is approximately 17 metres. This is because sound must travel to the reflecting surface and back, and the time gap between original and reflected sound must be at least 0.1 seconds for the human ear to perceive them as separate. Using speed of sound in air as 340 m/s, total distance = 340 × 0.1 = 34 m, so one-way distance = 17 m.
Why can sound not travel through vacuum?+
Sound is a mechanical wave that requires a medium (solid, liquid, or gas) to propagate. It travels by vibrating particles, which push neighboring particles, creating compressions and rarefactions. In a vacuum, there are no particles to vibrate or transfer energy, so sound cannot travel. This is why astronauts in space cannot hear each other without radios.
What is the difference between pitch and loudness?+
Pitch depends on the frequency of sound — higher frequency produces higher pitch (e.g., whistle) and lower frequency produces lower pitch (e.g., drum). Loudness depends on the amplitude of vibration — larger amplitude produces louder sound (e.g., shout), smaller amplitude produces softer sound (e.g., whisper). They are independent characteristics.
How does SONAR measure the depth of the ocean?+
SONAR sends ultrasound waves from a ship into the water. When the waves hit the seabed, they reflect back. The device records the time taken for the echo to return. Using the formula depth = (speed of sound in water × time) ÷ 2, it calculates the depth. The division by 2 accounts for the sound traveling down and back up.
What is ultrasound and what are its uses?+
Ultrasound is sound with frequency above 20,000 Hz, beyond human hearing range. Uses include: (i) Medical imaging like pregnancy scans and organ examination, (ii) Cleaning delicate parts and instruments, (iii) Detecting cracks in metal structures, (iv) SONAR technology for underwater navigation, and (v) Breaking kidney stones (lithotripsy).
What are the three main parts of the human ear?+
The three parts are: (i) Outer ear — includes pinna and ear canal, collects sound waves. (ii) Middle ear — contains eardrum and three ossicles (hammer, anvil, stirrup) that amplify vibrations. (iii) Inner ear — contains cochlea (fluid-filled spiral organ) with hair cells that convert vibrations into electrical signals sent to the brain.
What is the audible range of frequencies for humans?+
Humans can hear sound frequencies from 20 Hz to 20,000 Hz (20 kHz). Sounds below 20 Hz are called infrasound (e.g., earthquakes, elephant calls) and sounds above 20 kHz are ultrasound (e.g., used in medical imaging). The upper limit decreases with age; elderly people often cannot hear high-frequency sounds.
What is reverberation and how is it different from echo?+
Reverberation is the persistence of sound caused by multiple reflections in a confined space, where reflected sounds blend together and reach the ear within 0.1 seconds of each other, creating a prolonged, muddled sound. Echo is a distinct repetition of sound heard separately because the reflected sound reaches the ear at least 0.1 seconds after the original sound.
Why does sound travel faster in solids than in gases?+
Sound travels faster in solids because particles in solids are tightly packed and have strong intermolecular forces. Vibrations are transferred more efficiently from particle to particle. In gases, particles are far apart and move randomly, so energy transfer is slower. For example, sound travels at ~5000 m/s in steel but only ~343 m/s in air.
How can I score full marks in numerical problems on sound?+
Always write the given data clearly, state the formula you will use, substitute values with correct units, show the calculation step-by-step, and write the final answer with proper units and significant figures. Even if your final answer is slightly wrong, you will get method marks. Practice at least 10 echo and SONAR problems before the exam.

Related resources

Important Questions: CBSE Class 9 Physics Chapter 11 SoundClass 9 Physics Chapter 11 Sound — Formulas & Key PointsCBSE Class 9 Physics Chapter 11 Sound — 20 MCQs with Answersमहत्वपूर्ण प्रश्न: CBSE Class 9 Physics Chapter 11 SoundCBSE Class 9 Mathematics Chapter 1 Number Systems — NotesCBSE Class 9 Mathematics — Number Systems: complete chapter guideClass 9 Physics Chapter 7: Motion – Complete Notes, Definitions & ExamplesCBSE Class 9 Mathematics Chapter 1 Number Systems Worksheet with Answers

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