Viva Voce: Sound | Lab Manuals for Class 9 PDF Download

Q.1. How do human beings produce sound?

Due to the vibration of vocal cords.

Q.2. What is the speed of sound in air?

The speed of sound in air at 22^° C temperature is 344 m/s.

Q.3. How is the reverberation of sound reduced at home/auditorium?

By using sound absorbing materials like curtains, draperies, ceiling with fibre boards etc.

Q.4. Name two animals that can hear inffasonic sound.

Rhinoceroses, whales, and elephants.

Q.5. Give two examples of animals that can hear ultrasound.

Rats and bats.

Q.6. What is the audible range of sound for human beings?

The audible range of sound is 20 Hz to 20,000 Hz.

Q.7. What is reverberation?

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

Q.8. Can sound travel through the vacuum?

No

Q.9. What produces sound?

Vibration produces sound.

Q.10. Can sound be visualised as a wave? Why?

Yes, sound travels in a wave which causes disturbance in the medium particles, set them in motion and wave travels.

Q.11. What happens to the speed of sound if the medium is changed?

Speed of sound depends on the media in which it is travelling. Speed of sound is higher in solids, and lower in liquids and least in gases.

Q.12. Can you hear the reflected sound?

Yes, to hear the reflection of sound (echo) the time interval between the original sound and the reflected sound must be at least 0.1 second.

Q.13. How can you calculate the minimum distance for echo?

Speed of sound in air = distance / time
340 m/s = distance/0.1s
distance = 34.4 m
This is the total distance, hence half of 34.4 m is 17.2 m.

Q.14. Give two examples where multiple reflection is used.

In megaphones, curved ceilings or walls of the concert hall helps in creating multiple reflections of sound.

Q.15. If the incident sound wave makes an angle of 35° with the reflecting surface, what is the angle of reflection?

The angle of reflection is 55°.

Q.16. What are infrasound and ultrasound?

The sound with frequency less than 20 Hz are called infrasound waves. The sound with frequency higher than 20 kHz are called ultrasound waves.

Q.17. There are two tubes, A is wide and B is narrow, which one is suitable for stethoscope?

The narrow tube B is suitable for stethoscope as multiple reflection is more and sound can be heard distinctly.

Q.18. What is the minimum distance required for a person to hear the echo of his sound?

The reflecting surface should be at the distance of 17.2 nr from the person who would like to hear his echo distinctly.

Q.19. If the temperature of the medium is increased will that affect the speed of sound?

Yes, the speed of sound increases if the temperature of the medium is increased.

Q.20. Why sound waves are called mechanical waves?

As sound waves set the particles of the medium in motion so they are called mechanical waves.