CBSE – 9th Standard Science


Class 9 Question Bank Chapter 12 – Sound


Q1. What is Sound?

Ans. Sound is a form of energy which produces a sensation of hearing in our ears.

Q2. What do you mean by Vibration?

Ans. Vibration means a kind of rapid to and fro motion of an object.

Q3. How sound is produced?

Ans. Sound is produced by vibrating objects.

Q4. How sound of the human voice is produced?

Ans. The sound of the human voice is produced due to vibrations in the vocal cords.

Q5. What is medium?

Ans. The matter or substance through which sound is transmitted is called a medium.

Q6. What are the types of medium?

Ans. It can be solid, liquid or gas.

Q7. What is a wave?

Ans. A wave is a disturbance that moves through a medium when the particles of the medium set neighboring particles into motion.

Q8. What are mechanical waves?

Ans. Sound waves are characterized by the motion of particles in the medium and are called mechanical waves.

Q9. Which is the most common medium through which sound travels?

Ans. Air is the most common medium through which sound travels.

Q10. What is compression?

Ans. When a vibrating object moves forward, it pushes and compresses the air in front of it creating a region of high pressure. This region is called a compression.

Q11. What is rarefaction?

Ans. When the vibrating object moves backwards, it creates a region of low pressure called Rarefaction

Q12. What is Propagation?

Ans. Propagation of sound can be visualized as propagation of density variations or pressure variations in the medium.

Q13. How sound gets propagated?

Ans. Sound propagates in the medium as a series of compressions and rarefactions.

Q14. What are Longitudinal Waves?

Ans. In these waves the individual particles of the medium move in a direction parallel to

the direction of propagation of the disturbance.

Q15. What are Transverse waves?

Ans. A Transverse wave is the one in which the individual particles of the medium move about their mean positions in a direction perpendicular to the direction of wave propagation.

Q16. What are the characteristics of sound waves?

Ans. The characteristics of sound waves are Frequency, Amplitude, Speed.

Q17. What do you mean by Crest and Trough?

Ans. A peak is called the crest and a valley is called the trough of a wave.

Q18. What do you mean by Wavelength?

Ans. The distance between two consecutive compressions (C) or two consecutive rarefactions (R) is called the wavelength.

Q19. How is wavelength represented?

Ans. The wavelength is usually represented by λ (Greek letter lambda).

Q20. What is the S.I unit of wavelength?

Ans. Its SI unit is meter (m).

Q21. What is Oscillation?

Ans. The change in density from the maximum value to the minimum value, again to the maximum value, makes one complete oscillation.

Q22. What is Frequency?

Ans. The number of such oscillations per unit time is the frequency of the sound wave.

Q23. How Frequency is represented?

Ans. It is usually represented by ν (Greek letter, nu).

Q24. What is the S.I. unit of frequency?

Ans. Its SI unit is hertz (symbol, Hz).

Q25. What is time period of the wave?

Ans. The time taken by two consecutive compressions or rarefactions to cross a fixed point is called the time period of the wave.

Q26. How Time Period is represented?

Ans. It is represented by the symbol T.

Q27. What is the S.I. unit of time period?

Ans. Its SI unit is second (s).

Q28. What is a pitch?

Ans. How the brain interprets the frequency of an emitted sound is called its pitch.

Q29. What is a high pitch sound?

Ans. A high pitch sound corresponds to more number of compressions and rarefactions passing a fixed point per unit time.

Q30. What do you mean by amplitude of the sound wave?

Ans. The magnitude of the maximum disturbance in the medium on either side of the mean value is called the amplitude of the wave. It is usually represented by the letter A.

Q31. What is a Tone?

Ans. A sound of single frequency is called a tone.

Q32. What is a Note?

Ans. The sound which is produced due to a mixture of several frequencies is called a note.

Q33. What is the Intensity of the sound?

Ans. The amount of sound energy passing each second through unit area is called the intensity of sound.

Q34. On which property speed of sound depends?

Ans. The speed of sound depends on the properties of the medium through which it travels.

Q35. What is a Sonic boom?

Ans. When a sound, producing source moves with a speed higher than that of sound, it produces shock waves in air. The air pressure variation associated with this type of shock waves produces a very sharp and loud sound called the “sonic boom”.

Q36. What is needed for the reflection of Sound waves?

Ans. An obstacle of large size which may be polished or rough is needed for the reflection of sound waves.

Q37. What is an Echo?

Ans. If we shout or clap near a suitable reflecting object such as a tall building or a mountain, we will hear the same sound again a little later. This sound which we hear is called an echo.

Q38. Rolling of effect is due to which effect?

Ans. The rolling of thunder is due to the successive reflections of the sound from a number of reflecting surfaces, such as the clouds and the land.

Q39. What is reverberation?

Ans. The repeated reflection that results in this persistence of sound is called reverberation.

Q40. What should one do to reduce reverberation?

Ans. To reduce reverberation, the roof and walls of the auditorium are generally covered with sound-absorbent materials like compressed fiberboard, rough plaster or draperies.

Q41. What is a Stethoscope?

Ans. Stethoscope is a medical instrument used for listening to sounds produced within the body, chiefly in the heart or lungs.

Q42. What is the audible range of sound for human beings?

Ans. The audible range of sound for human beings extends from about 20 Hz to 20000 Hz.

Q43. What is infrasonic sound?

Ans. Sounds of frequencies below 20 Hz are called infrasonic sound or infrasound.

Q44. Give an example who uses infrasonic sound for communication?

Ans. Rhinoceroses communicate using infrasound of frequency as low as 5 Hz.

Q44. What is Ultrasonic sound?

Ans. Frequencies higher than 20 kHz are called ultrasonic sound or ultrasound.

Q45. Who produces Ultrasonic sound?

Ans. Ultrasound is produced by dolphins, bats and porpoises.

Q46. What are the applications of Ultrasound?

Ans. (i) Ultrasound is generally used to clean parts located in hard-to-reach places. (ii)Ultrasounds can be used to detect cracks and flaws in metal blocks.

Q47. What is echocardiography?

Ans. Ultrasonic waves are made to reflect from various parts of the heart and form the image of the heart. This technique is called ‘echocardiography’.

Q48. What is the full form of SONAR?

Ans. The acronym SONAR stands for Sound Navigation And Ranging.

Q49. What is SONAR?

Ans. Sonar is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects.

Q50. Why SONAR technique is used?

Ans. The sonar technique is used to determine the depth of the sea and to locate underwater hills, valleys, submarine, icebergs, sunken ship etc.

Q51. How the distance if the object calculated by SONAR technique?

Ans. The distance of the object that reflected the sound wave can be calculated by knowing the speed of sound in water and the time interval between transmission and reception of the ultrasound.

Q52. How EAR works?

Ans. Ear allows us to convert pressure variations in air with audible frequencies into electric signals that travel to the brain via the auditory nerve.

Q53. What is ‘Pinna’?

Ans. The outer ear is called ‘pinna’.

Q54. What is Ear drum?

Ans. At the end of the auditory canal there is a thin membrane called the ear drum or tympanic membrane.

Q55. How the vibrations are amplified?

Ans. The vibrations are amplified several times by three bones the hammer, anvil and stirrup in the middle ear.

Q56. What turns pressure variations into electric signals?

Ans. The pressure variations are turned into electrical signals by the cochlea.

Q57. Electric signals are sent to the brain via which nerve?

Ans. The electrical signals are sent to the brain via the auditory nerve.