Competency Based Questions Chapter 11 Sound

Hint: Infer and demonstrate that sound is produced due to vibration of different objects.

Question.1. The image shows a setup consisting of a tuning fork and a metallic ball suspended using a thread.cbe-questions-science-class-9-ch-11-q-1What happens when the metallic ball hits the tuning fork?

(a) The tuning fork vibrates the ball to produce sound.
(b) The tuning fork vibrates to-and-fro to produce sound.
(c) The tuning fork gets heated by the collision of the ball.
(d) The tuning fork generates heat by the vibrating to-and-fro.

Question.2. A student performs an experiment using the setup as shown.cbe-questions-science-class-9-ch-11-q-2The tin can is cut open from its bottom and a rubber sheet is stretched to cover it. A small mirror is glued to the rubber sheet. What would happen to the circular spot of light on the wall when the student speaks into the open end of the tin can?

(a) The sound produced vibrates the rubber diaphragm, which causes the movement of the light spot on the wall.
(b) The sound produced vibrates the rubber diaphragm, which causes the light spot to appear dim due to the scattering of light.
(c) The sound produced vibrates the surface of the mirror, which causes a change in the color of the light spot on the wall.
(d) The sound produced vibrates the walls of the tin can, which causes the light spot to appear diffused due to the scattering of light.

Ans.1. (b) The tuning fork vibrates to-and-fro to produce sound.
Ans.2. (a) The sound produced vibrates the rubber diaphragm, which causes the movement of the light spot on the wall.

Hint: Generalise that sound travels as successive compressions and rarefactions in the medium.

Question.3. The image shows a vibrating tuning fork producing sound in the air.cbe-questions-science-class-9-ch-11-q-3What can be inferred from the image?

(a) The air molecules move down when the prongs of tuning fork push the air and move up when the prongs of tuning fork move back.
(b) The air molecules move up when the prongs of tuning fork push the air and move down when the prongs of tuning fork move back.
(c) The air molecules decompress when the prongs of tuning fork push the air and compress when the prongs of tuning fork move back.
(d) The air molecules compress when the prongs of tuning fork push the air and decompress when the prongs of tuning fork move back.

Question.4. The image shows a rubber diaphragm kept near a vibrating tuning fork.cbe-questions-science-class-9-ch-11-q-4How would the tuning fork affect the rubber diaphragm?

(a) The rarified air from the vibrating tuning fork causes the diaphragm to vibrate, while the compressed air causes no movement.
(b) The compressed air from the vibrating tuning fork causes the diaphragm to vibrate, while the rarified air causes no movement.
(c) The compressed air from the vibrating tuning fork pushes the diaphragm to the right and rarified air pulls the diaphragm to the left.
(d) The rarified air from the vibrating tuning fork pushes the diaphragm to the right and compressed air pulls the diaphragm to the left.

Ans.3. (d) The air molecules compress when the prongs of tuning fork push the air and decompress when the prongs of tuning fork move back.
Ans.4. (c) The compressed air from the vibrating tuning fork pushes the diaphragm to the right and rarified air pulls the diaphragm to the left.

Hint: Relate frequency, amplitude and speed of a sound wave to determine its loudness and frequency.

Question.5. The image shows a speaker causing density variation in air.cbe-questions-science-class-9-ch-11-q-5Based on the image, what can be inferred about the characteristics of sound waves?

(a) The area of low density defines the wavelength of the sound wave.
(b) The area of high density defines the frequency of the sound wave.
(c) The rate at which density variations occur defines the frequency of the sound wave.
(d) The rate at which pressure varies with density of air defines the wavelength of the sound wave.

Question.6. The image shows the wave shape of four different sound.cbe-questions-science-class-9-ch-11-q-6What is true about the characteristics of these sounds?

(a) Sound wave A has higher frequency than sound waves B and D.
(b) Sound wave C has higher amplitude than sound waves A and D.
(c) Sound waves A and B have same frequency but different amplitudes.
(d) Sound wave A has higher amplitude and frequency than sound wave D.

Ans.5. (c) The rate at which density variations occur defines the frequency of the sound wave.
Ans.6. (d) Sound wave A has higher amplitude and frequency than sound wave D.

Hint: Interpret the graphical representation of sound waves to determine its frequency, amplitude, and speed.

Question.7. A pianist is playing several notes which was graphed by a scientist. The scientist has been told that the loudest notes have the highest amplitude. Among the following notes, which one is the loudest note:

(a) cbe-questions-science-class-9-ch-11-q-7-a(b) cbe-questions-science-class-9-ch-11-q-7-b(c) cbe-questions-science-class-9-ch-11-q-7-c(d) cbe-questions-science-class-9-ch-11-q-7-d

Question.8. Below is a wave form representation of a sound wave. cbe-questions-science-class-9-ch-11-q-8What is the amplitude of the sound wave represented below? (Speed of the sound 3.30\times 10^{4} m/s)

(a) 2 cm
(b) 4 cm
(c) 8 cm
(d) 10 cm

Ans.7. (a) cbe-questions-science-class-9-ch-11-q-7-aAns.8. (b) 4 cm

Hint: Relate properties of the medium through which sound travels to its speed.

Question.9. Which medium will have sound waves propagating at a higher speed?

(a) A liquid medium at 25°C temperature.
(b) A liquid medium at 50°C temperature.
(c) A gaseous medium at 50°C temperature.
(d) A gaseous medium at 25°C temperature.

Question.10. The table lists speed of sound in different media.cbe-questions-science-class-9-ch-11-q-10Based on the table, what characteristics of the medium affect the speed of sound?

(a) Increase in density of the medium increases the speed of sound.
(b) Decrease in density of the medium increases the speed of sound.
(c) Decrease in temperature of the medium increases the speed of sound.
(d) Increase in temperature of the medium decreases the speed of sound.

Ans.9. (b) A liquid medium at 50°C temperature.
Ans.10. (a) Increase in density of the medium increases the speed of sound.

Hint: Examine the paths of reflection of sound on different surfaces.

Question.11. The image shows reflection of sound by a polished wall.cbe-questions-science-class-9-ch-11-q-11Based on the image, what can be inferred about how sound reflects off the polished wall?

(a) The reflected sound follows the path of the incident sound.
(b) The angle of incidence (i) is equal to the angle of reflection (r).
(c) The angle of incidence (i) is smaller than the angle of reflection (r).
(d) The reflected sound follows a shorter path than that of the incident sound.

Question.12. The image shows reflection of sound on three different surfaces.cbe-questions-science-class-9-ch-11-q-12Based on the image, what can be inferred about how reflection of sound is affected on these surfaces?

(a) The scattering of sound increases with the increasing roughness of the surface.
(b) The scattering of sound decreases with the increasing roughness of the surface.
(c) The angle of reflection is greater than the angle of incidence in the rough surface.
(d) The angle of reflection is smaller than the angle of incidence in the intermediate surface.

Ans.11. (b) The angle of incidence (i) is equal to the angle of reflection (r).
Ans.12. (a) The scattering of sound increases with the increasing roughness of the surface.

Hint: Explain propagation of sound in a medium based on their knowledge of echo and reverberation.

Question.13. The image shows reflection of sound by a wall. cbe-questions-science-class-9-ch-11-q-13What change would cause reverberation of the sound?

(a) Polishing the surface of the wall.
(b) Erecting a wall behind the receiver.
(c) Placing the sender closer to the wall.
(d) Increasing the frequency of the emitted sound.

Question.14. The sensation of sound persists for 0.1 seconds in our brain. As a result, a clap near a tall building can be heard again. At what temperature of the air would the minimum distance required for differentiating the original sound of clap from its reflection be the greatest?

(a) 0°C
(b) 10°C
(c) 20°C
(d) 30°C

Ans.13. (b) Erecting a wall behind the receiver.
Ans.14. (d) 30°C

Hint: Classify audible range of sounds of different organisms into ultra and infra sounds.

Question.15. People of old age have trouble hearing certain frequencies of sound. Which range of frequencies is mostly heard by these people?

(a) 10 Hz – 1,000 Hz
(b) 20 Hz – 10,000 Hz
(c) 9,500 Hz – 20,000 Hz
(d) 20,000 Hz – 22,000 Hz

Question.16. The image shows the hearing ranges of various organisms.cbe-questions-science-class-9-ch-11-q-16Based on the image, which organism has ability to hear infrasound?

(a) bat
(b) cat
(c) dolphin
(d) elephant

Ans.15. (b) 20 Hz – 10,000 Hz
Ans.16. (d) elephant

Hint: Demonstrate an understanding of application of ultrasound waves in medical, defence and other fields.

Question.17. The image shows the use of ultrasound waves in treatment of kidney.cbe-questions-science-class-9-ch-11-q-17Based on the image, what is the advantage of using ultrasound waves to break the kidney stones?

(a) It prepares the kidney for removal of stones by surgery.
(b) It prevents the stones from forming again in the kidneys.
(c) It helps remove stones from the kidney without any surgery.
(d) It softens the tissues in the kidneys to allow for removal of stones.

Question.18. The image shows the use of ultrasound in a ship.cbe-questions-science-class-9-ch-11-q-18How does the ship locate the submarine using ultrasound waves?

(a) The ship measures the time taken by the reflected waves to determine the distance of the submarine.
(b) The ship senses the ultrasound waves passively emitted by the submarine while it moves near the ship.
(c) The ship detects the amplitude of the ultrasound waves which get scattered by the body of the submarine to determine its depth.
(d) The ship measures the change in the amplitude of the ultrasound waves after getting reflected by the submarine to determine its depth.

Ans.17. (c) It helps remove stones from the kidney without any surgery.
Ans.18. (a) The ship measures the time taken by the reflected waves to determine the distance of the submarine.

Hint: Explain the process of hearing in human beings.

Question.19. How does the human ear sense the fluctuations in the air pressure due to sound?

(a) The pinna collects sound from the surrounding and amplifies the pressure variations, which get transmitted to the anvil.
(b) The eardrum vibrates the bones inside the middle ear, which transmits the amplified pressure variations to the inner ear.
(c) The eardrum vibrates the cochlea inside the middle ear, which transmits the amplified pressure variations to the inner ear.
(d) The pinna collects sound from the surroundings and converts it into electrical signals, which are sent to the brain through the auditory nerve.

Question.20. The image shows the diagram of human ear.cbe-questions-science-class-9-ch-11-q-20Which part of the ear converts air pressure variations into electrical signals?

(a) anvil
(b) stirrup
(c) cochlea
(d) auditory nerve

Ans.19. (b) The eardrum vibrates the bones inside the middle ear, which transmits the amplified pressure variations to the inner ear.
Ans.20. (a) anvil

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