Sound (Physics)

Total Questions: 56

11. The walls of the hall, built for music concerts should: [U.P.P.C.S. (Mains) 2007]

Correct Answer: (d) Absorb sound
Solution:

The walls of the hall built for music concerts should absorb sounds. Most of the solid walls reflects the sound. If the walls of concert hall reflect the sound, then audiences hear the echo sound. So to avoid this, there is a need to built soft surface walls.

12. Which of the following is a cause of echo? [Jharkhand P.C.S. (Pre) 2023]

Correct Answer: (c) Reflection of sound
Solution:

An echo is a sound caused by the reflection of sound waves from a surface back to the listener. It is the reflection of sound, arriving at the listener sometime after the direct sound.

Echoes are a result of reflections when a sound wave comes into contact with a boundary, particularly a flat and hard surface. Basically a reflection of sound causes echo.

13. To hear a clear echo, the minimum distance between the reflecting surface and the observer should be: [U.P.P.C.S. (Mains) 2007]

Correct Answer: (d) 16.5 metre
Solution:

The repetition of sound produced due to the reflection from a large surface like wall, hill or mountain is called echo. Consider an observer is producing a sound and it gets reflected by an obstacle. The sound travel towards the observer and the observer hear the sound again.

Let ‘d’ be the distance between the observer and the obstacle, ‘v’ is the sound velocity and ‘t’ is the time taken by the sound to and fro motion, then the velocity of the sound is given by

14. How much should minimum distance be between the source of sound and reflecting surface, so that an echo can be heard clearly? [R.A.S./R.T.S.(Pre) 2007]

Correct Answer: (b) 17 metre
Solution:

The repetition of sound produced due to the reflection from a large surface like wall, hill or mountain is called echo. Consider an observer is producing a sound and it gets reflected by an obstacle. The sound travel towards the observer and the observer hear the sound again.

Let ‘d’ be the distance between the observer and the obstacle, ‘v’ is the sound velocity and ‘t’ is the time taken by the sound to and fro motion, then the velocity of the sound is given by

15. A sound wave has frequency of 4 kHz and its wavelength is 35 cm, then how much time will it take to travel a distance of 3 km? [Chhattisgarh P.C.S. (Pre) 2021]

Correct Answer: (b) 2.14 sec
Solution:

16. One important characteristic of sound is 'Pitch', which depends upon: [U.P.P.C.S. (Mains) 2017]

Correct Answer: (b) Frequency
Solution:

The sensation of frequency is commonly referred to as the pitch of the sound. A high pitch sound corresponds to a high-frequency sound wave and a low pitch sound corresponds to a low-frequency sound wave. High pitch means very rapid oscillation and 'low' pitch corresponds to slower oscillation.

17. Shrillness of sound is determined by: [68ᵗʰ B.P.S.C. (Pre) 2022]

Correct Answer: (c) wavelength of sound
Solution:

It is true that shrillness of sound is determined by its frequency but frequency and wavelength are inversely proportionate. So, it is also true to say that shrillness of sound depends on its wavelength.

For example, shorter the wavelength means higher the frequency and more shrill sound. Since frequency and wavelength are inseparably interlinked (velocity of sound = wavelength frequency and velocity of sound is constant in a medium), the correct answer is option (c).

18. Two astronauts cannot hear each other on the Moon's surface, because: [U.P.U.D.A./L.D.A. (Pre) 2002]

Correct Answer: (b) No atmosphere on the Moon.
Solution:

In order for sound to propagate from one place to another, it requires a medium or a fluid to move through. The air on the Earth allows sound waves to move from one point to another. However, there is vacuum on the surface of Moon. Thus, there is no sound on the Moon.

19. An astronaut cannot hear his companion at the surface of the Moon because: [U.P.P.C.S. (Mains) 2013]

Correct Answer: (c) There is no medium for sound propagation.
Solution:

In order for sound to propagate from one place to another, it requires a medium or a fluid to move through. The air on the Earth allows sound waves to move from one point to another. However, there is vacuum on the surface of Moon. Thus, there is no sound on the Moon.

20. Consider the following statements: [I.A.S. (Pre) 2007]

1. A flute of smaller length produces waves of lower frequency.

2. Sound travels in rocks in the form of longitudinal elastic waves only.

Which of the statements given above is/are correct?

Correct Answer: (d) Neither 1 nor 2
Solution:

A flute of long length produces the waves of higher wavelength, thus a flute of smaller length produces waves of higher frequency. Therefore statement 1 is not correct.

Sound is transmitted through gases, plasma and liquids as longitudinal waves. Through solids (eg. in rocks), however, it can be transmitted as both longitudinal waves and transverse waves. Thus statement 2 is also incorrect.