Sound Class 9 MCQ Questions and Answers PDF

Question 1: In gases a sound wave is________
(a) Longitudinal only
(b) Transverse only
(c) both A and B
(d) None of these
Answer: A) Longitudinal only
Explanation: In gases, sound travels as longitudinal waves where particles vibrate back and forth in the same direction as the wave.

Question 2: A body produces sound only if it is______
(a) Made of glass
(b) Made of aluminum
(c) Vibration
(d) Made of iron
Answer: C) Vibration
Explanation: Sound is produced by vibrations of a body, regardless of the material.

Question 3: If a wave completes 20 vibrations in 2.5s, then its frequency is_________
(a) 200 Hz
(b) 50 Hz
(c) 20 Hz
(d) 8 Hz
Answer: D) 8 Hz
Explanation: Frequency = Number of vibrations / Time = 20 / 2.5 = 8 Hz.

Question 4: On increasing the temperature, the speed of sound in air__________
(a) Increases
(b) Decreases
(c) Does not change
(d) First increases then becomes
Answer: A) Increases
Explanation: Sound travels faster at higher temperatures as molecules move more quickly.

Question 5: We can easily distinguish between the sounds of different singers even without seeing them. This is all due to the different quality or timber of their sounds. On what factor does the quality of sound depend?
(a) Wavelength
(b) Waveform
(c) Wave frequency
(d) Wave amplitude
Answer: B) Waveform
Explanation: The waveform determines the quality or timbre of sound, helping us differentiate sources.

Question 6: Which of the following can produce longitudinal as well as transverse waves under different conditions?
(a) Bats
(b) Slinky
(c) Tuning fork
(d) None of these
Answer: B) Slinky
Explanation: A slinky spring can generate both longitudinal and transverse waves when stretched and shaken.

Question 7: Frequency of infrasonic waves is _______ than the frequency of ultrasound waves.
(a) less
(b) more
(c) almost same
(d) none of the above
Answer: A) less
Explanation: Infrasonic waves have frequencies below 20 Hz, while ultrasound is above 20,000 Hz.

Question 8: When the sound gets reflected from a surface
(a) the angle of incidence < angle of reflection
(b) the angle of incidence = the angle of reflection
(c) the angle of reflection is equal to 90°
(d) the angle of incidence > angle of reflection
Answer: B) the angle of incidence = the angle of reflection
Explanation: Sound reflection follows the law of reflection, like light, where both angles are equal.

Question 9: The unit of quantity on which the pitch of the sound depends is__________
(a) Hertz
(b) Metre
(c) Metre/second
(d) Second
Answer: A) Hertz
Explanation: Pitch is determined by frequency, which is measured in hertz (Hz).

Question 10: The hump on the + y-axis is called crest_____
(a) The hump on the – y axis is called the crest
(b) The highest point on the hump on the + y-axis is called the crest
(c) The highest point on the hump on the – y axis is called the crest
(d) None of the above
Answer: B) The highest point on the hump on the + y-axis is called the crest
Explanation: The crest is the highest point of a wave on the positive y-axis in a waveform.

Question 11: Sound travels in air if_________
(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
Explanation: In sound waves, particles oscillate around their positions while the disturbance travels.

Question 12: In the region of compression or rarefaction, in a longitudinal wave the physical quantity which does not change is____________
(a) Pressure
(b) Mass
(c) Density
(d) Volume
Answer: B) Mass
Explanation: The mass of the medium does not change during the wave’s passage, though pressure and density do.

Question 13: Infrasound can be heard by_______
(a) dog
(b) bat
(c) rhinoceros
(d) human beings
Answer: C) rhinoceros
Explanation: Rhinoceroses can detect infrasound, which is below the hearing range of humans.

Question 14: Which of the following quantities is transferred during wave propagation?
(a) Energy
(b) Particles
(c) Speed
(d) Mass
Answer: A) Energy
Explanation: Waves transfer energy through the medium, not matter.

Question 15: Loudness or softness of a sound depends on__________
(a) Amplitude
(b) Frequency
(c) Type of a wave
(d) None of these
Answer: A) Amplitude
Explanation: Greater amplitude means louder sound, while smaller amplitude gives softer sound.

Question 16: Before playing the orchestra in a musical concert, a sitarist tries to adjust the tension and pluck the string suitably. By doing so, he is adjusting
(a) the intensity of sound only
(b) the 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
Explanation: The sitarist tunes the string to match the frequency for harmony.

Question 17: The speed of sound is greater in________
(a) Nickel
(b) Ethanol
(c) Air
(d) Sulphur dioxide
Answer: A) Nickel
Explanation: Sound travels fastest in solids like nickel due to tightly packed particles.

Question 18: If the pendulum oscillates 78 times in one minute then the frequency of that pendulum will be____________
(a) 2 Hz
(b) 1.5 Hz
(c) 1.3 Hz
(d) 1.2 Hz
Answer: C) 1.3 Hz
Explanation: Frequency = Number of oscillations / Time = 78 / 60 = 1.3 Hz.

Question 19: Children under the age of 5 years can hear sounds up to________
(a) 10 kHz
(b) 20 Hz
(c) 25 kHz
(d) 30 kHz
Answer: C) 25 kHz
Explanation: Young children can hear higher frequency sounds, up to 25 kHz.

Question 20: You must have seen the doctor checking the sounds produced in the chest or heartbeat of a patient using a medical instrument called a Stethoscope. On what principle does this Stethoscope work?
(a) Multiple refractions
(b) Multiple reflections
(c) Wave motion
(d) None of these
Answer: B) Multiple reflections
Explanation: Stethoscopes work by reflecting sound waves multiple times to amplify the sound.