Sound Waves Characteristics and Applications Class 9 MCQ Questions Science Chapter 10

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Class 9 Science Chapter 10 Sound Waves Characteristics and Applications MCQ

Sound Waves Characteristics and Applications MCQ

Class 9 Science Chapter 10 MCQ online test

Question 1.
Which of the following does not produce sound wave?
(A) Drum
(B) Birds
(C) TV
(D) Microwave oven
Answer:
(D) Microwave oven
Microwave oven is used to produce electromagnetic wave.

Question 2.
A mechanical wave can travel
(A) in a material medium but not in vacuum.
(B) in vacuum but not in a material medium.
(C) Both in vacuum and a material medium
(D) Neither in a material medium nor in vacuum.
Answer:
(A) in a material medium but not in vacuum.
Mechanical wave can travel through material medium but not in vacuum.

Question 3.
Sound travels in air, if [NCERT Exemplar]
(A) particles of medium travel from one place to another
(B) there is no moisture in the atmosphere
(C) disturbance moves
(D) both particles as well as disturbance travel from one place to another
Answer:
(C) disturbance moves
When sound travels in air, then only disturbances created by the vibration of particle moves from one place to other.

Question 4.
A light string is suspended from a hook which is attached to a 1 kg weight at its lower end. If the string is pulled and then released, the disturbance produced in the spring is
(A) pulse
(B) longitudinal wave
(C) transverse wave
(D) None of these
Answer:
(C) transverse wave
Transverse waves are produced in stretched string.

Question 5.
In the curve, half the wavelength is

(A) AB
(B) BD
(C) DE
(D) AE
Answer:
(B) BD
In the given curve, half of the wavelength will be BD.

Question 6.
The minimum distance in which a sound wave repeats itself is called
(A) frequency
(B) amplitude
(C) wavelength
(D) time period
Answer:
(C) wavelength
The minimum distance in which sound wave repeats itself is called wavelength.

Question 7.
A wave in slinky travelled to and fro in 5 s and the length of the slinky is 5m. What will be the velocity of the wave ?
(A) 10 m/s
(B) 5 m/s
(C) 2 m/s
(D) 25 m/s
Answer:
(C) 2 m/s
As the wave moves to and fro, so the total distance will be
d = 2 × 5 = 10 m
We have, time,
t = 5 s
Velocity = \(\frac{\text { Total distance }}{\text { Time }}\)
= \(\frac{10}{5}\) m/s = 2 m/s

Question 8.
The frequency of a source of sound is 200 Hz. How many times does it vibrate in 2 min ?
(A) 2400
(B) 24000
(C) 24500
(D) 2450
Answer:
(B) 24000
Given, frequency = 200 Hz
Number of oscillation in 1 s = 200
[because frequency represents number of oscillations in 1 s]
Number of oscillation in 2 min or 120 s = 200 × 120 = 24000.

Question 9.
When we change feeble sound to loud sound, we increase its
(A) frequency
(B) amplitude
(C) velocity
(D) wavelength
Answer:
(B) amplitude
The loudness or softness of a sound is determined by its amplitude. So for a loud sound, it must have higher amplitude.

Question 10.
Which of the following figures represent the soft sound?

I.

II.

(A) I
(B) II
(C) I and II both
(D) None of these
Answer:
(A) I
If the sound waves have a small amplitude, then sound will be faint or soft but if waves have a large amplitude, then the sound will be loud.

Question 11.
If the frequency is the same, waves from a sitar wire and a veena wire are distinguished by
(A) loudness
(B) pitch
(C) quality
(D) intensity
Answer:
(C) quality
It enables us to distinguish one sound from another having the same pitch and loudness.

Question 12.
A key of a mechanical piano struck gently and then struck again but much harder this time. In the second case,
(A) sound will be louder but pitch will not be different.
(B) sound will be louder and pitch will also be higher.
(C) sound will be louder but pitch will be lower.
(D) both loudness and pitch will remain unaffected.
Answer:
(A) sound will be louder but pitch will not be different.
When the key of a piano is struck harder, the sound will be louder as it vibrates with greater amplitude but the pitch will not be different as it does not depend on how hard the key is struck.

Question 13.
Before playing the orchestra in a musical concert, a sitarist tries to adjust the tension and pluck the string suitable. By doing so, he is adjusting [NCERT Exemplar]
(A) intensity of sound only
(B) amplitude of sound only
(C) frequency of the sitar string with the frequency of other musical instruments
(D) loudness of sound
Answer:
(C) frequency of the sitar string with the frequency of other musical instruments
The sitarist adjusts the frequencies of the sitar strings by adjusting the tensions in them.

Question 14.
A man’s voice and a woman’s voice is differ by its
(A) loudness
(B) pitch
(C) intensity
(D) amplitude
Answer:
(B) Pitch
Pitch is the characteristic of sound by which we can distinguish between different sounds of the same loudness.

Question 15.
Note is a sound [NCERT Exemplar]
(A) of mixture of several frequencies.
(B) of mixture of two frequencies only.
(C) of a single frequency.
(D) always unpleasant to listen.
Answer:
(A) of mixture of several frequencies.
The sound produced due to a mixture of several frequencies is called a note.

Question 16.
Which of the following statements is/are correct?
I. Sound would travel faster on a hot summer day than on a cold winter day.
II. Velocity of sound is directly proportional to the square of its absolute temperature.
(A) I and II
(B) Only I
(C) Only II
(D) None of these
Answer:
(A) I and II
The velocity of sound in a gas is directly proportional to the square root of its absolute temperature. Since, temperature of a hot day is more than cold winter day, therefore sound travel faster on a hot summer day than on a cold winter day.

Question 17.
Echo is caused by the phenomenon of
(A) reflection
(B) rarefaction
(C) refraction
(D) reverberation
Answer:
(A) reflection
An echo is the reflected sound waves.

Question 18.
A man is beating a drum infront of a cliff, hears the echo after 4s. What is the distance of man from the cliff, if velocity of sound in air is 330 m/S?
(A) 660 m
(B) 500 m
(C) 1000 m
(D) 0.3 km
Answer:
(A) 660 m
Given, speed = 330 m/s and
time = 4s As
we know that,
Distance, s = Speed × Time
= 330 × 4 = 1320 m
As in 4s, sound has to travel twice distance between man and the cliff.
So, distance between man and cliff is \(\frac{s}{2}\)
= \(\frac{1320}{2}\) = 660 m.

Question 19.
What is the SI unit of loudness?
(A) Dioptre
(B) Metre
(C) Weber
(D) Decibel
Answer:
(D) Decibel
The SI unit of loudness is decibel (dB).

Question 20.
What is the range of audio waves ?
(A) 20 kHz to 200 kHz
(B) 20 Hz to 20 kHz
(C) 20 Hz to 200 MHz
(D) 20 Hz to 20 MHz
Answer:
(B) 20 Hz to 20 kHz
The range of audio waves is 20 Hz to 20 kHz.

Question 21.
Infrasound can be heard by [NCERT Exemplar]
(A) dog
(B) bat
(C) rhinocerose
(D) human beings
Answer:
(C) rhinocerose
Infrasound is the waves whose frequency is less than 20 Hz. Rhinoceroses communicate using infrasound of frequency as low as 5 Hz.

Question 22.
In SONAR, we use [NCERT Exemplar]
(A) ultrasonic waves
(B) infrasonic waves
(C) radio waves
(D) audible sound waves
Answer:
(A) ultrasonic waves
In SONAR, we use ultrasonic waves or ultrasound.

Question 23.
Earthquake produces which kind of sound before the main shock wave begins [NCERT Exemplar]
(A) ultrasound
(B) infrasound
(C) audible sound
(D) None of these
Answer:
(B) infrasound
Earthquake produces infrasound before the main shock wave begins.

Question 24.
Infrasonic (f_i), audible (f_a) and ultrasonic (f_u) frequencies of sound are related as
(A) f_i < f_a < f_u
(B) f_a < f_i < f_u
(C) f_i > f_a > f_u
(D) f_a < f_u < f_i
Answer:
(A) f_i < f_a < f_u
Infrasonic, audible and ultrasonic frequencies of sound are related as f_i < f_a < f_u

Question 25.
Sound waves transfer
(A) energy
(B) matter
(C) Both (A) and (B)
(D) None of these
Answer:
(A) energy
Sound waves transfer energy through vibrations.

Question 26.
The image shows a set up consisting of a tuning fork and a metallic ball suspended using a thread.

What 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.
Answer:
(B) The tuning fork vibrates to and fro to produce sound.
When the metallic ball strikes the tuning fork, it starts vibrating, producing sound waves.

Question 27.
Which medium will have sound waves propagating at i 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.
Answer:
(B) A liquid medium at 50°C temperature.
Sound travels faster in liquids than in gases, and higher temperature increases speed because particles vibrate more rapidly.

Question 28.
Which wave property determines the loudness of sound?
(A) Frequency
(B) Pitch
(C) Speed
(D) Amplitude
Answer:
(D) Amplitude
Amplitude of a sound wave determines its loudness.

Question 29.
The sensation of sound persists for 0.1 s 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
Answer:
(D) 30°C
Speed of sound waves will be highest at 30°C which means it will take less time to get back to the person and hence it would be difficult to hear echo at a certain distance. So, the minimum distance has to be increase to compensate for the increased speed of sound.

Sound Waves Characteristics and Applications Class 9 Assertion and Reason Questions

Directions (Question Nos. 1 – 11): In each of the following questions, a statement of Assertion is given by the corresponding statement of Reason. Of the statements, mark the correct answer as
(A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
(B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
(C) Assertion is true, but Reason is false.
(D) Assertion is false, but Reason is true.

Question 1.
Assertion (A): A sound wave is a longitudinal wave.
Reason (R): Sound waves can be produced in all three media such as solids, liquids and gases.
Answer:
(B) Both Assertion and Reason are true, but Reason is not the correct explanation of Assertion.
Sound wave is longitudinal wave which requires a medium (solid, liquid or gas) to travel through them. Hence, Assertion and Reason both are true, but Reason is not the correct explanation of Assertion.

Question 2.
Assertion (A): Velocity of sound wave of frequency 550 Hz and wavelength 0.6 m is 330 m/s.
Reason (R): Velocity of sound wave is given by
Velocity = Frequency × Wavelength.
Answer:
(A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Velocity of sound wave = Frequency × Wavelength
= 550 × 0.6 = 330 m/s
Hence, Assertion and Reason both are true and Reason is the correct explanation of Assertion.

Question 3.
Assertion (A): On rainy day, sound travel slower than a dry day.
Reason (R): The density of air decreases when moisture is present in air.
Answer:
(D) Assertion is false, but Reason is true.
The density of moist air is less than the density of dry air. The speed of sound is inversely proportional to the square root of density of medium. So, sound travels faster on rainy days than on dry days.

Question 4.
Assertion (A): Pitch of sound is helpful to distinguish between a man’s voice and woman’s voice of the same loudness without seeing them.
Reason (R): Greater frequency of sound, the higher will be its pitch.
Answer:
(A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.

Pitch of sound depends on the frequency of vibration. Greater the frequency of a sound, the higher will be its pitch which helps to distinguish between a man’s voice and woman’s voice of the same loudness. Hence, Assertion and Reason both are true and Reason is the correct explanation of Assertion.

Question 5.
Assertion (A): Echo is caused by the phenomenon of reflection.
Reason (R): The persistance of a sound in a big hall is due to echo.
Answer:
(C) Assertion is true, but Reason is false.
Echo is caused by the phenomenon of reflection. The persistance of sound in a big hall is due to reverberation. Hence, Assertion is true, but Reason is false.

Question 6.
Assertion (A): The audible range of sound for human beings is from 20 Hz to 20000 Hz.
Reason (R): For a human being, it is difficult to hear ultrasonic sound while easy to hear infrasonic sound.
Answer:
(C) Assertion is true, but Reason is false.
A human being can hear only audible range of frequency (20 Hz to 20000 Hz) but cannot hear infrasonic and ultrasonic sound. Hence, Assertion is true, but Reason is false.

Question 7.
Assertion (A): Moths and bats move out freely even in night and search out prey.
Reason (R): Moths and bats send ultrasonic signals catch their prey.
Answer:
(A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Bats and moths send ultrasonic signals and receive it back after reflection from prey. Hence, both Assertion and Reason are correct and Reason is the correct explanation of Assertion.

Question 8.
Assertion (A): Elephants and rhinoceroses communicate using infrasonic sound which is not audible for normal human.
Reason (R): Sound of frequency below 20 Hz is called infrasound.
Answer:
(A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Elephants and rhinoceroses communicate using infrasound frequency of 5 Hz which is below 20 Hz and the audible frequency for human is 20 Hz to 20 kHz.

Question 9.
Assertion (A): Sound wave is an longitudinal wave.
Reason (R): Speed of sound in solid is less than air.
Answer:
(C) A is true, R is false.
Sound waves are indeed longitudinal, but the speed of sound is greater in solids than in air, not less.

Question 10.
Assertion (A): The loudness of sound is measured in decibel.
Reason (R): If sound waves have a large amplitude, then the sound will be loud.
Answer:
(B) Both A and R are true, but R is not the correct explanation of A.
Loudness is measured in decibel and higher amplitude means louder sound, but amplitude explains why sound is loud, not the unit of measurement.

Question 11.
Assertion (A): Ultrasonic sound is used in industry for detecting flaws (cracks etc) in metal blocks without damaging them.
Reason (R): An internal crack (or hole) reflects back the ultrasonic waves.
Answer:
(A) Both A and R are true and R is the correct explanation of A.
Ultrasound detects cracks because cracks cause reflection that reveals the flaw.