Sound

Total Questions: 56

41. 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]

(a) 10 metre
(b) 17 metre
(c) 24 metre
(d) 30 metre

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

v = 2 ×d / t
Substituting t= 1/10 sec, it is minimum time required to distinguish between two sounds for listening echo.

v=velocity of sound =330 m/sec at 20°C
then d = (v ×t)/2 = 1/2 × [330(1/10)]
=16.5 m (about 17 m).

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

(a) 21.4 sec
(b) 2.14 sec
(c) 12.4 sec
(d) 1.25 sec

Correct Answer: (b) 2.14 sec

Solution:The relation between the wavelength (λ) frequency (n) and velocity (v) can be given as

⇒v=n×λ

Given that:

⇒frequency (n)=4 KHz=4×10³ Hz

⇒wavelength (λ)=35 cm = 0.35 m;

⇒distance (D)= 3 km =3×10³ m

⇒hence the velocity of the sound wave (v)=n×λ

⇒4×10³ ×0.35

⇒1.4×10³ m/sec

⇒now time (t)=distance /velocity

⇒3×10³ /1.4×10³ =2.14

thus the given sound wave will take 2.14 sec to travel a distance of 3 km.

43. One important characteristic of sound is pitch which depends upon : [U.P. P.C.S. (Mains) 2017]

(a) Intensity
(b) Frequency
(c) Quality
(d) Amplitude

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.

44. Shrillness of sound is determined by ; [68th B.P.S.C. (PRE) 2022]

(a) velocity of sound
(b) amplitude of sound
(c) wavelength of sound
(d) more than one of the above
(e) none of the above

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 (wavelength, frequency and velocity of sound is constant in a medium), the correct answer is option (c).

45. Two astronaut cannot hear each other on the moon,s surface because : [U.P.U.D.A/L.D.A.(PRE) 2002]

(a) their ears have stopped working on the moon.
(b) no atmosphere on the moon.
(c) they wear special space suits on the moon.
(d) the sound travels much more slowly on moon.

Correct Answer: (b) no atmosphere on the moon.

Solution:In order for sound to propagate from one place to another, it requires a medium 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.

46. An astronaut cannot hear his companion at the surface of the moon because : [U.P.P.C.S.(MAINS) 2013]

(a) produced frequency are above the radio frequency.
(b) temperature is too low during night and too high during day.
(c) there is no medium for sound propagation.
(d) there are many craters on the surface of the moon.

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

47. Consider the following statements: [L.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?

(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

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, solid 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.

48. Consider the following statements: [I.A.S. (PRE) 2023]

1. In a seismograph, P waves are recorded earlier than S waves.
2. In P waves, the individual particles vibrate to and fro in the direction of wave propagation whereas in S waves, the particles vibrate up and down at right angles to the direction of wave propagation
which of the following statement given above is/are correct:

(a) 1 only
(b) 2 only
(c) both 1 and 2
(d) neither 1 nor 2

Correct Answer: (c) both 1 and 2

Solution:Seismic waves are vibrations in the Earth that transmit energy and occur during seismic activity such as earthquakes, volcanic eruptions, and even man-made explosions. There are two types of seismic waves, primary waves and secondary waves. Primary waves, also known as P waves or pressure waves, are longitudinal compression waves similar to the motion of a slinky. Thus, in P waves, the individual particles vibrate to and fro in the direction of wave propagation. P waves can travel through liquids, solids and gases. Secondary waves, or S waves which can only travel through solids, are slower than P waves and therefore, in a seismograph P waves are recorded earlier than S waves. The motion secondary waves is perpendicular to the direction of the travel, similar to the motion of vigorously shaking a Thus, in S waves, the particles vibrate up and down at angles of 90º to the direction of wave propagation. Hence, both statements are correct.

49. Consider the following statements about ultrasonic waves : [U.P.P.C.S.(MAINS) 2004]

1. They can destroy insects.
2. They can clean clothes by removing dust.
3. They can be used to treat diseases.
4. They can control automatic doors.
Of the above statements:

(a) 1 and 2 are correct.
(b) 3 and 4 correct.
(c) 1, 2 and 3 are correct.
(d) all the correct.

Correct Answer: (d) all the correct.

Solution:Sound waves are divided into three categories that different frequency range: Audible waves (20 Htz-20000 Htz), Infrasonic waves (<20 Htz) and Ultrasonic wave (>20,000 Htz). Ultrasonic waves are used to destroy insects, clean clothes by removing dust, treat diseases, control automatic doors, detection of aircraft and submarine determination of depth of sea etc.

50. Ultrasonics are sound waves of frequency : [U.P.P.C.S.(pre) 2012]

(a) greater than 20000 hz.
(b) less than 10000 hz.
(c) equal to 1000 hz.
(d) none of these.

Correct Answer: (a) greater than 20000 hz.

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Sound

Sound

41. 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]

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

43. One important characteristic of sound is pitch which depends upon : [U.P. P.C.S. (Mains) 2017]

44. Shrillness of sound is determined by ; [68th B.P.S.C. (PRE) 2022]

45. Two astronaut cannot hear each other on the moon,s surface because : [U.P.U.D.A/L.D.A.(PRE) 2002]

46. An astronaut cannot hear his companion at the surface of the moon because : [U.P.P.C.S.(MAINS) 2013]

47. Consider the following statements: [L.A.S. (Pre) 2007]

48. Consider the following statements: [I.A.S. (PRE) 2023]

49. Consider the following statements about ultrasonic waves : [U.P.P.C.S.(MAINS) 2004]

50. Ultrasonics are sound waves of frequency : [U.P.P.C.S.(pre) 2012]

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