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All questions of Sound & Human Ear for Grade 9 Exam

Sound is produced by _________objects.
  • a)
    fast moving
  • b)
    vibrating
  • c)
    stationary
  • d)
    rotating
Correct answer is option 'B'. Can you explain this answer?

Anchal Singh answered
It vibrates, which, in turn, causes the air around it to vibrate. The vibration of air causes your eardrum to vibrate in tune with the vibrating air. This is interpreted by your brain as sound.

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Which of the following is a mechanical wave?
  • a)
    Sound
  • b)
    Light
  • c)
    Radio waves
  • d)
    X-rays
Correct answer is option 'A'. Can you explain this answer?

Arjun Sharma answered
Electromagnetic waves do not require a medium in order to transport their energy. Mechanical waves are waves that require a medium in order to transport their energy from one location to another. Because mechanical waves rely on particle interaction in order to transport their energy, they cannot travel through regions of space that are void of particles. That is, mechanical waves cannot travel through a vacuum. This feature of mechanical waves is often demonstrated in a Physics class. A ringing bell is placed in a jar and air inside the jar is evacuated. Once air is removed from the jar, the sound of the ringing bell can no longer be heard. The clapper is seen striking the bell; but the sound that it produces cannot be heard because there are no particles inside of the jar to transport the disturbance through the vacuum. Sound is a mechanical wave and cannot travel through a vacuum.

Echo is not heard in a room of 10 m x 10 in x 10 m dimension due to (speed of sound in air = 300 m/s)
  • a)
    reflection
  • b)
    absorption
  • c)
    persistence
  • d)
    humidity
Correct answer is option 'C'. Can you explain this answer?

Hansa Sharma answered
If you have persistence, you continue to do something even though it is difficult or others are against it. 
( As the sensation of sound persists in our brain for about 0.1 s, to hear a distinct echo the time interval between  the original sound and the reflected one must be at least 0.1 s. If we take the speed of the sound to be 300 m/s at a given temperature, in air, sound must go to the obstacle and reach back the ear of the listener on reflection after 0.1s. )

Which waves are employed in SONAR?
  • a)
    X rays
  • b)
    Ultrasonic 
  • c)
    Sonar wave
  • d)
    Infrasonic Wave
Correct answer is option 'B'. Can you explain this answer?

Abhishek Kumar Verma answered
》ULTRASONIC WAVE # Because this WAVE has high frequency (above 20000 Hz). * IN SHORT * - High frequency means HIGH PENETRATING POWER.

Ultrasound is not used to:
  • a)
    detect defective foetus.
  • b)
    find the distance of the building.
  • c)
    clean spiral tubes.
  • d)
    as a tool in the treatment of muscular pain.
Correct answer is option 'B'. Can you explain this answer?

Vijay Midha answered
When bats detect ultrasonic waves which after touching the prey comes back to bats ear which tell them how far their prey is and how it looks like. Similarly people detect ultrasonic waves to know the distance. the waves touch the building and comes back which tells us how far it is.
hope it helps you

Young children below 5 year can hear up to a frequency of
  • a)
    25 KHz
  • b)
    20 KHz
  • c)
    40 KHz
  • d)
    30 KHz
Correct answer is option 'A'. Can you explain this answer?

Vikram Khanna answered
The children under age 5 years have a fully developed inner and middle ears allowing them to hear from 20 Hz to 25,000 Hz. As the age increases, our inner ear changes gradually which cause reduce in hearing capacity from 20 Hz to 20,000 Hz.

The motion of the particles of a medium when a sound wave is passing through it is:
  • a) 
    translatory
  • b) 
    random
  • c) 
    rotatory
  • d) 
    oscillatory
Correct answer is option 'D'. Can you explain this answer?

Razia Shaik answered
The motion of the particles of a medium when a sound wave is passing through it is oscillatory because the particles move forward set the neighbouring particle into motion and then come back to it's original position. The particles move to and fro which is also called oscillatory motion.

Sound of single frequency is called
  • a)
    Noise
  • b)
    Tone
  • c)
    Note
  • d)
    Music
Correct answer is option 'B'. Can you explain this answer?

Jyoti Kapoor answered
A sound of single frequency is called a tone. A sound that is produced when several frequencies are mixed is called a note. For example a musical note has tones of various frequencies (sounds of different pitch) and amplitudes (loudness). A note has many component waves in it whereas a tone is represented by a single wave form. 

Which part of the ear amplifies the vibrations of eardrum?
  • a)
    hammer, anvil and stirrup
  • b)
    Pinna
  • c)
    Cochlea
  • d)
    Auditory nerves
Correct answer is option 'C'. Can you explain this answer?

Anchal Singh answered
The area of tympanic membrane is about 90mm2 but only 45 to 55 mm2 is effective for sound conduction. This area is much higher than that of oval window ie membrane of inner ear which has an area of about 3.1 mm2 . It acts as an acoustic transformer for sound conduction and amplifies whatever sound is incident onto it giving an advantage of 51/3 ~ 17 : 1.
It also forms a barrier which protects from the allergic infective and irrative substances.

A stethoscope utilizes the principle of
  • a)
    reverberation
  • b)
    multiple reflection of sound
  • c)
    conservation of energy
  • d)
    none
Correct answer is option 'B'. Can you explain this answer?

Rounak Basu answered
Introduction:
A stethoscope is a medical instrument used by healthcare professionals to listen to the sounds produced by the body. It consists of a diaphragm and a set of tubes that transmit sound from the patient's body to the healthcare provider's ears. The stethoscope utilizes the principle of multiple reflection of sound to amplify and transmit the sounds effectively.

Explanation:
The principle of multiple reflection of sound is based on the fact that sound waves can bounce off surfaces and travel in different directions. This principle is used in the design of the stethoscope to enhance the detection and transmission of sound waves.

How does a stethoscope work?
1. Sound generation: When a patient's body produces sound, such as the beating of the heart or the movement of air in the lungs, the sound waves travel through the body.

2. Diaphragm and tubes: The diaphragm of the stethoscope is placed against the patient's body, allowing the sound waves to enter the instrument. The sound waves then travel through the tubes, which act as conduits for the sound.

3. Reflection of sound: Inside the tubes, the sound waves undergo multiple reflections. These reflections occur when the sound waves encounter the inner surfaces of the tubes. Each reflection helps to amplify the sound waves, making them louder and more distinct.

4. Transmission to the healthcare provider's ears: After the sound waves have undergone multiple reflections, they eventually reach the healthcare provider's ears through the earpieces of the stethoscope. The sound waves are now amplified and easily detectable by the healthcare provider.

Advantages of utilizing the principle of multiple reflection of sound:
- Amplification of sound: The multiple reflections of sound waves within the stethoscope tubes help to amplify the sound, making it easier for healthcare providers to hear and interpret the sounds produced by the body.

- Noise reduction: The design of the stethoscope, utilizing multiple reflections, helps to reduce external noise interference. The reflections of sound waves within the tubes help to isolate and enhance the desired sound signals, while minimizing background noise.

- Improved sound transmission: By utilizing the principle of multiple reflection, the stethoscope ensures efficient transmission of sound waves from the patient's body to the healthcare provider's ears. This helps in accurate diagnosis and monitoring of the patient's condition.

Conclusion:
The stethoscope utilizes the principle of multiple reflection of sound to amplify and transmit the sounds produced by the body. By incorporating this principle into its design, the stethoscope enhances the detection and transmission of sound waves, enabling healthcare providers to accurately diagnose and monitor their patients.

A top makes 16 rotations about its own axis within 0.4 seconds, its frequency is:
  • a)
    40 Hz
  • b)
    4 Hz
  • c)
    0.4 Hz
  • d)
    400 Hz
Correct answer is option 'A'. Can you explain this answer?

Nitya Tiwari answered
Frequency of a Top's Rotation

Definition of Frequency:
Frequency is defined as the number of oscillations or cycles per unit time.

Calculating Frequency:
To calculate frequency, we use the formula:

frequency = number of cycles/time taken

In this case, the top makes 16 rotations in 0.4 seconds. Therefore, the frequency of the top is:

frequency = 16/0.4 = 40 Hz

Thus, the correct answer is option A, which is 40 Hz.

The upper frequency limit of the audible range of human hearing is about
  • a)
    20 kHz
  • b)
    2000 Hz
  • c)
    2 kHz
  • d)
    2,000,000 Hz
Correct answer is option 'A'. Can you explain this answer?

Vipin T answered
Yes, bcoz humans can hear sounds of frequency between 20hz to 20000hz.
1000hz=1khz
20000hz=20khz
Thus the upper limit of the audible range of human hearing is 20khz.

The method of detecting the presence, position and direction of motion of distant objects by reflecting a beam of sound waves is known as _____.
  • a)
    RADAR
  • b)
    SONAR
  • c)
    MIR
  • d)
    CRO
Correct answer is option 'B'. Can you explain this answer?

Arjun Sharma answered
Sonar (originally an acronym for SOund Navigation And Ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels. Two types of technology share the name "sonar": passive sonar is essentially listening for the sound made by vessels; active sonar is emitting pulses of sounds and listening for echoes. Sonar may be used as a means of acoustic location and of measurement of the echo characteristics of "targets" in the water. Acoustic location in air was used before the introduction of radar. Sonar may also be used in air for robot navigation, and SODAR (an upward looking in-air sonar) is used for atmospheric investigations. The term sonar is also used for the equipment used to generate and receive the sound. The acoustic frequencies used in sonar systems vary from very low (infrasonic) to extremely high (ultrasonic). The study of underwater sound is known as underwater acoustics or hydroacoustics.

The wavelength of the sound produced by a tuning fork of frequency 450 Hz which is set to vibrate in air (take velocity of sound in air as 320 m/s) is
  • a)
    144 cm
  • b)
    0.07 m
  • c)
    7.1 cm
  • d)
    0.711 m
Correct answer is 'D'. Can you explain this answer?

Jaideep Sharma answered
Given:
Frequency of tuning fork (f) = 450 Hz
Velocity of sound in air (v) = 320 m/s

To find:
Wavelength of sound produced by the tuning fork

Formula:
Wavelength (λ) = v/f

Calculation:
Substituting the given values in the formula, we get:
λ = v/f
λ = 320/450
λ = 0.711 m

Therefore, the wavelength of the sound produced by the tuning fork of frequency 450 Hz in air is 0.711 m.

Infrasonic fi Audible fa and Ultrasonic fu sounds are related a 
  • a)
    fi < fa < fu
  • b)
    fa < fi < fu
  • c)
    fi > fa > fu
  • d)
    fa < fu < fi
Correct answer is option 'A'. Can you explain this answer?

Hansa Sharma answered
Sound is only audible to the average humar ear if the frequencies lie between 20 Hz and 20 kHz. The actual range varies from person to person. Sound waves with frequencies less than 20 Hz are called infrasonic or subsonic and those with frequencies above 20 kHz are called ultrasonic. 

Absorbent materials are to be used while making interior design in an auditorium as
  • a)
    echo is to be increased
  • b)
    To prevent reverberation 
  • c)
    it has to look good
  • d)
    sound travels with a lesser velocity 
Correct answer is option 'B'. Can you explain this answer?

Ananya Das answered
Absorptive material on the back and side walls will help reduce the reverberation time and unwanted reflections. If possible, try to avoid parallel surfaces, which can cause flutter echoes.

Sound waves in air are
  • a)
    transverse
  • b)
    longitudinal
  • c)
    electromagnetic
  • d)
    polarised
Correct answer is option 'B'. Can you explain this answer?

Arvind Singh answered
Longitudnal waves travel in the form of compression and rarefactions. In the waves the individual particles of the medium move in a direction parallel to the direction of the propagation of the distirbance. The particles do not move from one place to another but they simply oscillate back and forth about their position of rest. This is exactly how a sound wave propagates. Hence, sound waves are longitudnal waves. 

What is the difference between a low pitched and high pitched sound?
  • a)
    high pitched sound has a higher frequency than low pitched sound
  • b)
    high pitched sound has a larger amplitude
  • c)
    low pitched sound has a larger amplitude
  • d)
    both sounds have same frequency but different amplitudes
Correct answer is option 'A'. Can you explain this answer?

Ravi Verma answered
A low pitch has a lower frequency. A high pitch has a higher frequency.
You can describe frequency with a unit called ‘Hertz’, which means per second. So vibrations per second.
A lower pitch has a longer wavelength and a higher pitch has a shorter wavelength.

Sound travels fastest in
  • a)
    air
  • b)
    vacuum
  • c)
    steel
  • d)
    water
Correct answer is option 'C'. Can you explain this answer?

Sounak Sarkar answered
Sounds travel fastest in solid. As steel is the only solid in the options, steel is the correct option.

The vibrations or the pressure variations inside the inner ear are converted into electrical signals by the:
  • a)
    Nerves
  • b)
    Hammer, anvil and stirrup
  • c)
    Cochlea
  • d)
    Pinna
Correct answer is option 'C'. Can you explain this answer?

Jyoti Kapoor answered
In the inner ear, the pressure variations are turned into electrical signals by the cochlea. These electrical signals are sent to the brain via the auditory nerve, and the brain interprets them as sound.

“Due to the high power of ultrasound waves. It is used for breaking and cutting objects” The above statement is
  • a)
    True
  • b)
    Partially false.
  • c)
    Partially True
  • d)
    False
Correct answer is option 'A'. Can you explain this answer?

Jay Kulkarni answered
Ultrasound waves vibrate at frequency higher than 20,000Hz. Vibration at such a high speed can be used to breaking and cutting objects like stone in kidney.

Sound cannot travel throug
  • a)
    air
  • b)
    water
  • c)
    iron
  • d)
    space
Correct answer is option 'D'. Can you explain this answer?

Rishita Choudhary answered
Sound is not travel inSpace because in space their is no atmosphere. space is a vaccum.

On which quantity does the pitch of the sound depend?
  • a)
    Frequency
  • b)
    Amplitude
  • c)
    Speed
  • d)
    wavelength
Correct answer is option 'A'. Can you explain this answer?

Kiran Rane answered
Introduction:
The pitch of a sound refers to its perceived frequency. It is a subjective perception that allows us to differentiate between high and low sounds. The frequency of a sound wave is the number of vibrations or cycles it completes in one second and is measured in Hertz (Hz). The pitch of a sound depends solely on its frequency, and this is what distinguishes a high-pitched sound from a low-pitched sound.

Explanation:
The pitch of a sound can be understood by considering the following points:

1. Frequency:
- The pitch of a sound is directly related to its frequency.
- Frequency refers to the number of vibrations or cycles a sound wave completes in one second.
- When the frequency of a sound wave is high, the pitch is perceived as high, and when the frequency is low, the pitch is perceived as low.

2. Relationship between Frequency and Pitch:
- The relationship between frequency and pitch can be understood by considering musical notes.
- In a musical scale, higher notes are produced by vibrations with higher frequencies, while lower notes are produced by vibrations with lower frequencies.
- For example, the note 'A' above middle C on a piano has a frequency of 440 Hz, while the note 'C' one octave below has a frequency of 261.63 Hz.
- The higher the frequency, the higher the pitch perceived by our ears.

3. Perception of Pitch:
- Our ears are sensitive to a wide range of frequencies, and we perceive different pitches based on the frequency of the sound waves.
- The human audible range typically extends from about 20 Hz to 20,000 Hz.
- Sounds with frequencies below 20 Hz are referred to as infrasound, and those above 20,000 Hz are referred to as ultrasound, which are not audible to humans.

Conclusion:
In conclusion, the pitch of a sound depends solely on its frequency. A high-pitched sound is characterized by a high frequency, while a low-pitched sound is characterized by a low frequency. The relationship between frequency and pitch can be observed in musical notes, where higher notes have higher frequencies and lower notes have lower frequencies. Our ears perceive these frequency differences as differences in pitch, allowing us to differentiate between high and low sounds.

A compression is a region of
  • a)
    high frequency
  • b)
    high pressure
  • c)
    low frequency
  • d)
    low pressure
Correct answer is option 'B'. Can you explain this answer?

Ananya Sharma answered
However instead of crests and troughs, longitudinal waves have compressions and rarefactions. A compression is a region in a longitudinal wave where the particles are closest together. A rarefaction is a region in a longitudinal wave where the particles are furthest apart.

The velocity of ultrasonic sound in water is 1400 m. The depth of the ocean as detected by SONAR, if the time taken to receive the reflected wave is 15s, is
  • a)
    1050 m
  • b)
    105 m
  • c)
    10.5 km
  • d)
    21 km
Correct answer is option 'C'. Can you explain this answer?

Anika Reddy answered
Given:
Velocity of ultrasonic sound in water = 1400 m/s
Time taken to receive the reflected wave = 15 s

To find:
Depth of the ocean detected by SONAR

Formula:
Distance = Velocity × Time

Calculation:
Using the given formula, we can calculate the distance traveled by the sound wave.

Distance = Velocity × Time
Distance = 1400 m/s × 15 s
Distance = 21000 m

Now, we need to convert the distance into kilometers. Since 1 km = 1000 m, we can divide the distance by 1000 to get the distance in kilometers.

Distance in kilometers = Distance in meters / 1000
Distance in kilometers = 21000 m / 1000
Distance in kilometers = 21 km

Therefore, the depth of the ocean as detected by SONAR is 21 km.

Which of the following quantities is transferred during wave propagation?
  • a)
    Energy
  • b)
    Particles
  • c)
    Speed
  • d)
    Mass
Correct answer is option 'A'. Can you explain this answer?

Anita Menon answered
A wave can be thought of as a disturbance or oscillation that travels through space-time, accompanied by a transfer of energy. The direction a wave propagates is perpendicular to the direction it oscillates for transverse waves. A wave does not move mass in the direction of propagation; it transfers energy.

A source produces 20 crests and 20 troughs in 0.2 second. Find the frequency of the wave.
  • a)
    200Hz
  • b)
    150Hz
  • c)
    100Hz
  • d)
    1Hz
Correct answer is option 'C'. Can you explain this answer?

Srijita answered
One oscillation = 1 crest & 1 trough 20 crest & 20 trough = 20 oscillation Time = 0.2 sec Frequency = No. of oscillation/Time = 20/0.2 = 200/2 = 100 Hz

X – rays, light rays are electromagnetic waves is a
  • a)
    True statement
  • b)
    False statement
  • c)
    Partially false
  • d)
    Partially True
Correct answer is option 'A'. Can you explain this answer?

Paridhi Shah answered
Understanding Electromagnetic Waves
Electromagnetic waves are a fundamental concept in physics, and both X-rays and light rays fall under this category. Here's a detailed explanation:
X-rays and Light Rays
- X-rays and light rays are both forms of electromagnetic radiation.
- They are part of the electromagnetic spectrum, which ranges from radio waves to gamma rays.
Characteristics of Electromagnetic Waves
- All electromagnetic waves travel at the speed of light in a vacuum.
- They consist of oscillating electric and magnetic fields that are perpendicular to each other and the direction of wave propagation.
Differences in Energy and Wavelength
- X-rays have much higher energy and shorter wavelengths compared to visible light.
- While visible light has a wavelength of approximately 400 to 700 nanometers, X-rays can have wavelengths ranging from 0.01 to 10 nanometers.
Applications and Importance
- X-rays are commonly used in medical imaging to view bones and internal organs.
- Light rays are essential for vision and are utilized in various technologies like photography and lighting.
Conclusion
The statement that "X-rays and light rays are electromagnetic waves" is indeed true. Both belong to the same family of waves characterized by their electromagnetic nature, differing mainly in their energy levels and wavelengths. Understanding this classification helps in grasping the broader concepts of physics and their applications in real-world scenarios.

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