MCQ Questions of Sound With Solutions Class 9

Physics CBSE Class 9 MCQS On Sound with Solutions.

1. On slinky we can produce :

(A) Transverse waves only

(B) Longitudinal waves only

(D) Neither transverse nor longitudinal waves

Ans. (C)

Sol. We can produce both transverse and logitudinal waves.

2. A pulse is a disturbance :

(A) of short duration

(B) of long duration

(D) Which travels in gases only

Ans. (A)

Sol. A pulse is of short duration disturbance

3. A Big explosion on the moon cannot be heard on the earth because :

(A) The explosion produces high frequency sound waves which are inaudiable

(B) Sound waves require material medium for propagation

(D) Sound waves are absorbed in earth’s atmosphere

Ans. (B)

Sol. Sound waves require medium to travel.

4. Which of the following waves cannot travel through vacuum :

(A) Light waves

(B) Heat waves

(D) Sound waves

Ans. (D)

Sol. Sound waves require medium to travel.

5. An astronout cannot hear his companion at surface of the moon because :

(A) Produced frequency are above the audio frequencies

(B) There is no medium for sound propagation

(D) These are too many crates on the surface of moon

Ans. (B)

Sol. At surface of moon no medium for propagation

6. Distance of crest from mean position is called :

(A) Amplitude

(B) Frequency

(D) Wave length

Ans. (A)

Sol. Amplitude

7. The frequency of wave is expressed in :

(A) Seconds

(B) Cycle

(D) Metre per second

Ans. (C)

Sol. Frequency of waves is equal to cycles/second

8. In the region of compression in longitudinal wave, the density of particles of the medium :

(A) Increases

(B) Decreases

(D) None of these

Ans. (A)

Sol. In compression density of particle is maximum

9. The linear distance between the compression and the next rarefaction is 0.8m. The wavelength of the longitudinal wave is :

(A) 0.8 m

(B) 1.6 m

(D) 3.2 m

Ans. (B)

Sol. Wavelength is distance between two compression or two rarefaction so after compression their is a rarefaction so wavelength is 0.8 × 2 ⇒ 1.6 m

10. A SONAR receives ultrasonic waves after 3 seconds when they are sent inside the sea water. What is the depth of the reflecting object if speed of ultrasonic waves is 1500 m/s in sea water :

(A) 1500 m

(B) 4500 m

(D) 2750 m

Ans. (C)

Sol. speed = $\frac{{{\rm{Distance}}}}{{{\rm{time}}}}$

1500 = $\frac{{2 \times d}}{3}$

d = $\frac{{1500 \times 3}}{7}$

d = 2250

distance = 2250 m

11. A stone is dropped in a well of depth 500 m and a sound is heard after $\frac{{{\rm{80}}}}{{\rm{7}}}$ seconds. Then speed of sound is : [g = 10 m/s²]

(A) 300 m/s

(B) 350 m/s

(D) 330 m/s

Ans. (B)

Sol. speed = $\frac{{2 \times {\rm{distance}}}}{{{\rm{time}}}}$

$\Rightarrow$ $= \frac{{2 \times 500}}{{80}} \times 7\,\, \Rightarrow \,\,350\,{\rm{m/s}}$

12. The distance between a crest and the next trough in a periodic wave is :

(A) l

(B) $\frac{\lambda }{2}$

(D) 2l

Ans. (B)

Sol. The distance between a crest and next through is half of the wavelength i.e. $\frac{\lambda }{2}$

13. Speed of sound in rainy season is :

(A) more

(B) less

(D) May or may not change

Ans. (A)

Sol. Speed of sound is dependent upon medium, so it is more in rainy season.

14. A long flexible spring is called :

(A) Spring balance

(B) Slinky

(D) None

Ans. (B)

Sol. A long flexible spring is called slinky and tension in it is directly proportional to its extension or compression.

15. Which is true for a wave :

(A) fT = 1

(B) $\frac{f}{T} = 1$

(D) None

Ans. (A)

Sol. For a wave $f\, = \,\frac{1}{T}$

or $fT\, = \,1$

16. The speed of sound in air :

(A) Decreases with increase in temperature

(B) Increases with increase in temperature

(D) Remain the same with decrease in temperature.

Ans. (B)

Sol. Speed of sound in air increases with increase in temperature.

17. Which of the following statements is correct :

(A) Both sound and light waves in air are longitudinal

(B) Both sound waves and light waves in air are transverse

(D) Sound waves in air are longitudinal while light waves are transverse

Ans. (D)

Sol. Sound waves are longitudinal waves and light waves are transverse.

18. Mechanical waves (sound waves) in a gas are :

(A) Transverse

(B) Longitudinal

(D) Either transverse or longitudinal

Ans. (B)

Sol. Longitudinal waves

19. Ultrasonic, Infrasonic and Audible waves travel through a medium with speed V_u, V_i and Va resp then:

(A) V_i = V_a = V_u

(B) V_u > V_a > V_i

(D) V_a ≤ V_u= V_i

Ans. (A)

Sol. All have equal speed

20. Which of the following does not require medium to propagate :

(A) Radio-waves

(B) Water-waves

(D) Waves in string

Ans. (A)

Sol. Radio waves are electro magnetic waves.

21. The relation between frequency (f) wavelength ( $\lambda$ ) and velocity of propogation (V) of a wave is :

(A) f = V $\lambda$

(B) f = $\lambda$ /V

(D) f = $\frac{1}{{V\lambda }}$

Ans. (C)

Sol. v = f × l

f = v/l

22. A boat at anchor is reached by waves whose crests are 100m apart and whose velocity is 25 m/sec. These waves strike the boat once every :

(A) 2500 sec

(B) 0.25 sec

(D) 4 sec

Ans. (D)

Sol. V = $f \times \lambda$

V = $\lambda /T$

T = $\lambda /V$ = $\frac{{100}}{{25}} = 4\,{\rm{sec}}{\rm{.}}$

23. The wavelength of sound from a tuning fork of frequency 330 Hz is nearly :

(A) 100 cm

(B) 10 cm

(D) 330 cm

Ans. (A)

Sol. Speed of sound is 330 m/s

V = $f \times \lambda$

$\Rightarrow$ $\frac{{330}}{{330}}$ = $\lambda = 1m = 100\,{\rm{cm}}$

24. Elastic waves in solids are :

(A) Transverse

(B) Longitudinal

(D) Neither transverse nor longitudinal

Ans. (C)

Sol. Elastic waves in solids can be transverse like waves in a string and can be longitudinal like sound waves.

25. The distance between two consecutive compressions is 1.4 m. The wave length of the wave is :

(A) 2.8 m

(B) 1.4 m

(D) 4.2 m

Ans. (B)

Sol. Distance between two compressions is wavelength.

26. Name the quality of sound waves which enable you to differentiated between sound of different persons :

(A) Loudness

(B) Timbre

(D) Wavelength

Ans. (B)

27. Which is true for a wave :

(A) fT = 1

(B) $\frac{f}{T} = 1$

(D) None

Ans. (A)

Sol. frequency = $\frac{1}{{{\rm{Time}}\,{\rm{period}}}}$

$\Rightarrow$ f × T = 1

28. Unit of time period of a wave is :

(A) Hz

(B) Metre

(D) None

Ans. (C)

Sol. Unit of time period is second.

29. Which is not true for wave :

(A) Wave velocity V = $f\lambda$

(B) Energy is transferred during wave motion

(D) Unit of wave velocity is m/s

Ans. (C)

Sol. All waves cannot pass through vaccum like sound wave.

30. The linear distance between the compression and the next rarefactions is 0.8m. The wavelength of the longitudinal wave is :

(A) 0.8 m

(B) 1.6 m

(D) 3.2 m

Ans. (B)

Sol. Wavelength is distance between two compression or two rarefaction so after compression there is a rarefaction so wavelength is 0.8 × 2⇒ 1.6 m

31. Pitch of A is more than that of B, then frequency of :

(A) A = B

(B) A > B

(D) none

Ans. (B)

Sol. Pitch of sound depends upon its frequency. More the frequency, higher pitched will be the sound.

32. The speed of electromagnetic wave in air is :

(A) 3 × 10⁵ km/s

(B) 3 × 10⁷ km/s

(D) 3 × 10⁸ km/s

Ans. (A)

Sol. All electromagnetic wave travel in air with speed of light i.e. 3 × 10⁵ km/s

33. A vibrator strikes the water 20 times a second. The frequency of the waves produced is :

(A) 20 Hz

(B) 10 Hz

(D) 40 Hz

Ans. (A)

Sol. frequency = $\frac{{{\rm{Cycles}}}}{{{\rm{sec}}}}$ or $\frac{{{\rm{Oscillation}}}}{{{\rm{sec}}}}$

= 20 Hz

34. A periodic wave is characterized by :

(A) Phase only

(B) Wavelength only

(D) All of these

Ans. (D)

Sol. Periodic wave have all three attributes.

35. Waves produced due to the earth quake are known as :

(A) Seismic waves

(B) Infrasonic waves

(D) None of these

Ans. (A)

Sol. Due to earth quake Seismic wave are produced.

36. Waves produced by Supersonic jet planes are :

(A) Shock waves

(B) Infrasonic waves

(D) None of these

Ans. (A)

Sol. Supersonic jet planes produces shock wave.

37. Hertz stands for :

(A) Second

(B) Second^-1

(D) Metre^-1

Ans. (B)

Sol. Frequency have unit hertz i.e. 1/sec. or sec^–1

38. What is transferred in wave motion :

(A) Energy

(B) Particles

(D) None of these

Ans. (A)

Sol. Energy is transferred in wave motion.

39. Compression are the points of :

(A) Maximum displacement

(B) Maximum density

(D) Can’t say

Ans. (B)

Sol. Compression are the point of maximum density.

40. 1KHz is equal to :

(A) 10 Hz

(B) 100 Hz

(D) 10000 Hz

Ans. (C)

Sol. 1kHz =1000 Hz

41. An object will produce sound only if it is :

(A) In gaseous state

(B) In solid state

(D) In liquid state

Ans. (C)

Sol. Vibration of molecules is necessary for production of sound.

42. Drum produces sound due to :

(A) Blowing

(B) Plucking

(D) Rubbing

Ans. (C)

Sol. Drum produces sound due to striking.

43. When sound waves travelling in air enter into the medium of water, the quantity which remains unchanged is :

(A) Wavelength

(B) Velocity

(D) None

Ans. (C)

Sol. Frequency is constant.

44. On Moon, sound is :

(A) Like a thunder

(B) Inaudible

(D) None

Ans. (B)

Sol. Sound require medium to travel so, at moon sound is in audible.

45. Sound takes some time to travel from one place to another. It will be maximum :

(A) At night

(B) During winter

(D) Nothing can be said

Ans. (B)

Sol. During winter sound is maximum because sound require medium to travel

46. Sound waves in air are :

(A) Longitudinal waves

(B) Radio waves

(D) Electromagnetic waves

Ans. (A)

Sol. Sound waves is longitudinal wave.

47. Sound waves can not pass through :

(A) A solid liquid mixture

(B) A liquid gas mixture

(D) A perfect vacuum

Ans. (D)

Sol. Sound cannot pass through vacuum.

48. A sound wave is travelling from east to west. In which direction do the molecules in the air move :

(A) East to West

(B) North to South

(D) South to North

Ans. (A)

Sol. In sound wave molecules travel in same direction of sound wave.

49. Sound waves can travel :

(A) Only in solids

(B) Only in liquid

(D) In all of these

Ans. (D)

Sol. Sound travels in all three media.

50. The speed of sound is maximum in :

(A) Air

(B) Hydrogen

(D) Iron

Ans. (D)

Sol. Speed of sound is maximum in solid.

51. An echo is heard if the minimum distance between the source of sound and the obstacle is :

(A) 1m

(B) 11 m

(D) 17 m

Ans. (D)

Sol. 17m is minimum distance to produce echo.

52. A boy blows a whistle while standing infront of a cliff. He hears the echo after 0.2 sec. The distance of cliff from the boy is [if velocity of sound is 332 m/s] :

(A) 33.2 m

(B) 33.2 cm

(D) 66.4 cm

Ans. (A)

Sol. V = $\frac{{2d}}{{time}}[{\rm{for echo]}}$

332 = $\frac{{20 \times d}}{2}$

d = 33.2 m

53. Echo is produced due to :

(A) Reflection of sound

(B) Refraction of sound

(D) None of thesedreamweaver 8

Ans. (A)

Sol. Echo is produce due to reflection of sound.

54. Sonar is based on the principle of :

(A) Echo

(B) Reverberation

(D) Any one of the above

Ans. (A)

Sol. Sonar is based on Echo.

55. The echo is heard if the original sound reflected by an obstacle reaches our ears after :

(A) 10s

(B) 5s

(D) 0.1 s

Ans. (D)

Sol. 1/10 second is required for echo.

56. When a sound producing source moves with a speed greater than the speed of sound then :

(1) It produces shock waves

(2) It produces sonic boom

(3) Sound source is said to be travelling at super sonic speed

(4) Sound source is said to be travelling at ultrasonic speed

(A) Only 1 is correct

(B) 1, 2 & 4 are correct

(D) All are correct

Ans. (C)

Sol. It produce shock wave, sonic boom, and travell at super sonic speed.

57. RADAR makes the use of :

(A) Radio waves of very long wave length

(B) Radio waves of very short wave length

(D) Ultra violet waves of longer wavelengths

Ans. (B)

Sol. Radar uses radio waves of small wavelength.

58. Name an animal which navigates and finds food by echo location :

(A) Bat

(B) Owl

(D) Parrot

Ans. (A)

Sol. Bat.

59. The part of ear which is filled with a liquid is the :

(A) Cochlea

(B) Ear canal

(D) Hammer

Ans. (A)

Sol. Cochlea.

60. Unit to measure the level of noise in a perticular area :

(A) Mol

(B) Decibel

(D) None of these

Ans. (B)

Sol. Intensity is measured in decibel.

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