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Important Questions (1 mark): Sound - Class 9 MCQ


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25 Questions MCQ Test Science Class 9 - Important Questions (1 mark): Sound

Important Questions (1 mark): Sound for Class 9 2024 is part of Science Class 9 preparation. The Important Questions (1 mark): Sound questions and answers have been prepared according to the Class 9 exam syllabus.The Important Questions (1 mark): Sound MCQs are made for Class 9 2024 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Important Questions (1 mark): Sound below.
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Important Questions (1 mark): Sound - Question 1

Sound energy is basically:

Detailed Solution for Important Questions (1 mark): Sound - Question 1
Sound Energy:
Sound energy refers to the energy produced by the vibrations of particles in a medium, which then propagate as waves through that medium. It is a form of mechanical energy, as it involves the movement of particles in a substance.
Explanation:
Sound energy can be further understood by breaking it down into its key components:
1. Mechanical Energy: Sound energy is a type of mechanical energy because it involves the movement and vibration of particles in a substance. When an object vibrates, it creates waves of compression and rarefaction in the surrounding medium, which then propagate as sound waves.
2. Electromagnetic Energy: Sound is not considered electromagnetic energy because it does not involve the propagation of electromagnetic waves. While sound waves can affect the particles in a medium, they do not involve the transfer of energy through electromagnetic fields.
3. Potential Energy: Sound energy is not a form of potential energy. Potential energy refers to the energy possessed by an object due to its position or state. Sound energy, on the other hand, is related to the motion of particles and the transfer of that motion as waves.
4. Electrical Energy: Sound energy is also not electrical energy. Electrical energy refers to the energy carried by electric charges, such as in the flow of electrons through a conductor. Sound energy does not involve the flow of electrical charges but rather the movement of particles in a medium.
In conclusion, sound energy is a form of mechanical energy resulting from the vibrations and movements of particles in a medium. It is not electromagnetic energy, potential energy, or electrical energy.
Important Questions (1 mark): Sound - Question 2

The transfer of energy in a material medium due to the periodic motion of its particles is called:

Detailed Solution for Important Questions (1 mark): Sound - Question 2
Wave Motion and Velocity of Waves. Wave motion. It is a disturbance which travels in a material medium through the repeated periodic motion of the particles of the medium about their mean position.
Important Questions (1 mark): Sound - Question 3

Which is not the condition for hearing sound?

Detailed Solution for Important Questions (1 mark): Sound - Question 3
Explanation:
The condition for hearing sound involves several factors that work together to allow us to perceive sound waves. However, one of these conditions does not directly contribute to the process of hearing sound. Let's break down each condition and explain why it is or isn't necessary for hearing sound:
A: There must be a vibrating body capable of transferring energy:
- This condition is necessary because sound is produced by vibrations. When an object vibrates, it creates compressions and rarefactions in the surrounding medium, which we perceive as sound waves. Without a vibrating body, there would be no sound to hear.
B: There must be a material medium to pick up and propagate energy:
- This condition is necessary because sound waves require a medium to travel through. Sound waves cannot travel through a vacuum, as they rely on the molecules or particles of a medium to transmit the vibrations. Without a material medium, there would be no way for sound waves to propagate and reach our ears.
C: The medium must have a large density:
- This condition is not necessary for hearing sound. The density of the medium does not affect our ability to hear sound. Sound waves can travel through different densities of materials, such as air, water, or solids. The speed of sound may vary depending on the density of the medium, but it does not impact our ability to perceive sound.
D: There must be a receiver to receive the energy and interpret it:
- This condition is necessary because without a receiver, such as our ears, we would not be able to detect and interpret sound waves. Our ears are designed to detect the vibrations in the air and convert them into electrical signals that our brain can interpret as sound.
In conclusion, the correct answer is C: The medium must have a large density. While the other conditions are necessary for hearing sound, the density of the medium does not directly affect our ability to perceive sound.
Important Questions (1 mark): Sound - Question 4

An instrument commonly used in laboratory to produce a sound of some particular frequency is :

Detailed Solution for Important Questions (1 mark): Sound - Question 4

The correct answer is C as Tuning fork is an instrument used to produce sound in fixed frequency in laboratories. A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs formed from a U-shaped bar of elastic metal .

Important Questions (1 mark): Sound - Question 5

The sound waves in a medium are characterised by the:

Detailed Solution for Important Questions (1 mark): Sound - Question 5
A wave is a disturbance that moves through a medium when the particles of the medium set neighboring particles into motion. Since sound waves are characterized by the motion of particles in the medium, they are Mechanical Waves.
Important Questions (1 mark): Sound - Question 6

The sound waves which travel in the air are called:

Detailed Solution for Important Questions (1 mark): Sound - Question 6
Do not conclude that sound is a transverse wave that has crests and troughs. Sound waves traveling through air are indeed longitudinal waves with compressions and rarefactions. As sound passes through air (or any fluid medium), the particles of air do not vibrate in a transverse manner.
Important Questions (1 mark): Sound - Question 7

When a sound wave travels in the air, the physical quantity which is transferred from one place to the other is:

Detailed Solution for Important Questions (1 mark): Sound - Question 7
Basically sound is mechanical energy which is passed on from one to another particle. 
Important Questions (1 mark): Sound - Question 8

In case of longitudinal waves, the particles of medium vibrate:

Detailed Solution for Important Questions (1 mark): Sound - Question 8
Introduction:
Longitudinal waves are a type of mechanical waves where the particles of the medium vibrate parallel to the direction of wave propagation. Understanding how the particles of the medium move is essential in comprehending the nature of longitudinal waves.
Detailed Explanation:
In the case of longitudinal waves, the particles of the medium vibrate in the same direction as the wave propagation. This means that the particles move back and forth along the same line as the wave travels.
To understand this concept more clearly, let's consider a common example of a longitudinal wave, such as a sound wave traveling through air:
- When a sound wave is produced, it propagates through the air in the form of compressions and rarefactions.
- During compressions, the air particles are pushed closer together, resulting in an increase in air pressure.
- As the compressions move through the medium, the particles in the air vibrate in the same direction as the wave propagation. This means that the particles move towards each other and then away from each other, repeatedly.
- During rarefactions, the air particles move farther apart, resulting in a decrease in air pressure.
- The motion of the particles in the air, in response to the sound wave, is parallel to the direction in which the sound wave is traveling.
Therefore, the correct answer is A: In the direction of wave propagation.
Important Questions (1 mark): Sound - Question 9

In case of transverse waves the particles of a medium vibrate:

Detailed Solution for Important Questions (1 mark): Sound - Question 9
Explanation:
When discussing transverse waves, it is important to understand how the particles of a medium vibrate. Transverse waves are characterized by particles oscillating perpendicular to the direction of wave propagation. This means that the particles move in a direction that is at right angles to the direction in which the wave is moving.
Here is a detailed explanation of each option:
A: In the direction of wave propagation:
- This option is incorrect for transverse waves. In transverse waves, the particles do not vibrate in the same direction as the wave is moving.
B: Opposite to the direction of wave propagation:
- This option is also incorrect for transverse waves. The particles do not vibrate in the opposite direction of the wave propagation.
C: At right angles to the direction of wave propagation:
- This option is correct for transverse waves. The particles of the medium vibrate perpendicular to the direction of wave propagation.
D: None of the above:
- This option is incorrect. The correct answer is option C, as explained above.
In conclusion, the correct answer is C: "At right angles to the direction of wave propagation."
Important Questions (1 mark): Sound - Question 10

A longitudinal waves consists of:

Detailed Solution for Important Questions (1 mark): Sound - Question 10
Explanation:
A longitudinal wave consists of compressions and rarefactions in the medium. Here is a detailed explanation of these terms:
- Longitudinal Wave: A longitudinal wave is a type of wave in which the particles of the medium vibrate parallel to the direction of the wave's propagation. Examples of longitudinal waves include sound waves and seismic waves.
- Compression: In a longitudinal wave, a compression is a region where the particles of the medium are close together. It is a high-pressure region characterized by an increased density of particles.
- Rarefaction: On the other hand, a rarefaction is a region in a longitudinal wave where the particles of the medium are spread apart. It is a low-pressure region characterized by a decreased density of particles.
- Relationship: In a longitudinal wave, compressions and rarefactions alternate as the wave propagates through the medium. The particles in the medium oscillate back and forth, creating areas of compression and rarefaction.
Therefore, the correct answer is B: Compressions and rarefactions in the medium. A longitudinal wave consists of compressions and rarefactions as it propagates through the medium.
Important Questions (1 mark): Sound - Question 11

A transverse wave consists of:

Detailed Solution for Important Questions (1 mark): Sound - Question 11
Transverse Wave consists of:
- Crests and troughs in the medium: In a transverse wave, the particles of the medium vibrate perpendicular to the direction of wave propagation. This results in the formation of crests and troughs.
- Compressions and rarefactions in the medium: This statement is incorrect. Compressions and rarefactions are characteristics of longitudinal waves, not transverse waves. In longitudinal waves, the particles of the medium vibrate parallel to the direction of wave propagation, causing regions of compression and rarefaction.
- Both (A) and (B): This statement is incorrect as only option A, crests and troughs, is true for transverse waves.
- Neither (A), nor (B): This statement is incorrect as option A, crests and troughs, is true for transverse waves.
Therefore, the correct answer is option A: Crests and troughs in the medium.
Important Questions (1 mark): Sound - Question 12

The longitudinal waves can propagate only in :

Detailed Solution for Important Questions (1 mark): Sound - Question 12
Because it always flow through a medium, since in longitudinal waves the molecules transfer the energy of the propagation to the nearby molecules.Since we know that molecules are present in the solid, liquids and gases, therefore it can propagate in all these states.
Important Questions (1 mark): Sound - Question 13

Which of the following metal/s is/are not ductile?

Detailed Solution for Important Questions (1 mark): Sound - Question 13

To determine which metal/s is/are not ductile, we need to examine each option and identify their ductility properties.
Arsenic & Antimony:
- Both arsenic and antimony are considered brittle metals, meaning they lack ductility and are prone to fracturing when subjected to tension or bending forces.
Barium & Boron:
- Barium is a highly ductile metal, meaning it can be easily stretched into wires without breaking.
- Boron, on the other hand, is a non-metal and does not exhibit ductility.
Sodium & Iron:
- Sodium is a soft and malleable metal that can be easily deformed and stretched into wires, indicating its ductile nature.
- Iron is also a ductile metal and can be drawn into wires without breaking.
Copper:
- Copper is a highly ductile metal and is widely used in electrical wiring due to its ability to be easily drawn into thin wires.
Therefore, based on the above analysis, the metal/s that are not ductile are arsenic and antimony (option A).
Important Questions (1 mark): Sound - Question 14

A part of the longitudinal wave in which particles of medium are closer than the normal particles is called:

Detailed Solution for Important Questions (1 mark): Sound - Question 14
Compression:
- A compression is a part of a longitudinal wave where the particles of the medium are closer together than their normal positions.
- It is a region of high pressure and high particle density.
- In a compression, the particles are pushed together, resulting in an increase in density and pressure.
- The particles in a compression move in the same direction as the wave.
- Compressions are typically represented by the peaks or high points on a wave diagram.
Rarefaction:
- Rarefaction is the opposite of compression.
- It is a part of a longitudinal wave where the particles of the medium are spread apart, creating a region of low pressure and low particle density.
- In a rarefaction, the particles are farther apart than their normal positions.
- The particles in a rarefaction move in the opposite direction of the wave.
- Rarefactions are typically represented by the troughs or low points on a wave diagram.
Crest:
- A crest is a high point or peak on a wave.
- It is the highest point of a transverse wave or the highest point of a longitudinal wave when represented graphically.
- In a longitudinal wave, crest refers to the high points where the particles are temporarily closer together.
- Crests are associated with regions of high pressure and high particle density.
Trough:
- A trough is a low point on a wave.
- It is the lowest point of a transverse wave or the lowest point of a longitudinal wave when represented graphically.
- In a longitudinal wave, trough refers to the low points where the particles are temporarily spread apart.
- Troughs are associated with regions of low pressure and low particle density.
In summary, the correct answer is D: Compression. It is the part of a longitudinal wave where particles of the medium are closer together than their normal positions, resulting in high pressure and high particle density.
Important Questions (1 mark): Sound - Question 15

In the compression region of the medium in case of longitudinal wave:

Detailed Solution for Important Questions (1 mark): Sound - Question 15
Explanation:
In the compression region of a medium in the case of a longitudinal wave, the following changes occur:
1. Volume momentarily decreases:
- When a compression wave passes through a medium, the particles of the medium are pushed closer together.
- This compression causes a temporary decrease in the volume of the medium.
- The particles move closer to each other in the direction of the wave propagation.
2. Density momentarily increases:
- As the particles of the medium are pushed closer together, the mass per unit volume increases.
- This increase in mass per unit volume is known as density.
- Therefore, in the compression region, the density of the medium momentarily increases.
3. Pressure momentarily increases:
- The compression of the medium leads to an increase in the number of particles in a given volume.
- As a result, the collisions between the particles increase, resulting in an increase in pressure.
- Therefore, in the compression region, the pressure of the medium momentarily increases.
4. All of the above:
- The compression of the medium in a longitudinal wave leads to a decrease in volume, an increase in density, and an increase in pressure.
- Therefore, all of the above options A, B, and C are correct.
In conclusion, in the compression region of a longitudinal wave, the volume momentarily decreases, the density momentarily increases, and the pressure momentarily increases.
Important Questions (1 mark): Sound - Question 16

A part of longitudinal wave in which particles of medium are farther away than the normal particles is called:

Detailed Solution for Important Questions (1 mark): Sound - Question 16
Longitudinal Waves and Rarefaction:
A longitudinal wave is a wave in which the particles of the medium vibrate in the same direction as the wave itself. It consists of compressions and rarefactions, which are regions of high and low pressure respectively.
The rarefaction is a part of the longitudinal wave where the particles of the medium are farther apart than their normal positions. Let's explore this concept in more detail:
Rarefaction:
- Rarefaction is a region in a longitudinal wave where the particles of the medium are spread apart.
- It is the opposite of compression, where particles are close together.
- In a rarefaction, the particles have moved away from their equilibrium position.
- The density of the medium in a rarefaction is lower than its normal density.
- It is represented by a trough-like shape in a waveform.
Comparison with other wave components:
- Trough: A trough is a low point on a transverse wave, not a longitudinal wave. It is not the correct answer in this case.
- Compression: A compression is a region in a longitudinal wave where the particles of the medium are close together. It is the opposite of rarefaction.
- Crest: A crest is a high point on a transverse wave, not a longitudinal wave. It is not the correct answer in this case.
Conclusion:
The correct answer is A: Rarefaction. In a longitudinal wave, rarefaction refers to the part where particles are farther apart than their normal positions. It is a region of low pressure and lower density compared to the rest of the medium.
Important Questions (1 mark): Sound - Question 17

In case of a longitudinal wave, in the region of rarefaction :

Detailed Solution for Important Questions (1 mark): Sound - Question 17
Explanation:
In the region of rarefaction of a longitudinal wave, the particles of the medium are spread out or have a lower density than in the equilibrium position. This results in several changes in the wave parameters.
The changes in the region of rarefaction are:
- The volume momentarily increases: The particles in the rarefaction region move away from each other, causing an increase in the volume of the medium. This is because the particles are spread out and have more space between them.
- The density momentarily decreases: As the particles move apart, the density of the medium in the rarefaction region decreases. This is because there are fewer particles per unit volume in the rarefaction region compared to the equilibrium position.
- The pressure momentarily decreases: The decrease in density in the rarefaction region leads to a decrease in pressure. As the particles move apart, there are fewer collisions between them, resulting in a lower pressure compared to the equilibrium position.
Therefore, all of the above changes occur in the region of rarefaction of a longitudinal wave.
Important Questions (1 mark): Sound - Question 18

In the region of compression or rarefaction, in a longitudinal wave the physical quantity which does not change is:

Detailed Solution for Important Questions (1 mark): Sound - Question 18
Answer:

  • Introduction:

  • In a longitudinal wave, such as a sound wave, there are regions of compression and rarefaction. During compression, the particles of the medium are pushed closer together, while during rarefaction, the particles spread apart. In this question, we are asked to identify the physical quantity that remains constant in these regions.


  • Explanation:

  • In a longitudinal wave, the physical quantity that does not change in the regions of compression or rarefaction is mass. Here's why:



    • Pressure: In the regions of compression, the particles are pushed closer together, leading to an increase in pressure. In the regions of rarefaction, the particles spread apart, resulting in a decrease in pressure. Therefore, pressure changes in these regions.

    • Density: Density is defined as mass per unit volume. In the regions of compression, the particles are pushed closer together, leading to an increase in density. In the regions of rarefaction, the particles spread apart, resulting in a decrease in density. Therefore, density changes in these regions.

    • Volume: In the regions of compression, the particles are pushed closer together, resulting in a decrease in volume. In the regions of rarefaction, the particles spread apart, leading to an increase in volume. Therefore, volume changes in these regions.

    • Mass: The mass of the particles remains the same in both the regions of compression and rarefaction. The compression or rarefaction does not affect the mass of the particles.


  • Conclusion:

  • Therefore, in a longitudinal wave, the physical quantity that does not change in the regions of compression or rarefaction is mass.


Important Questions (1 mark): Sound - Question 19

A slinky can produce in laboratory :

Detailed Solution for Important Questions (1 mark): Sound - Question 19

A slinky can easily demonstrate the two basic types of waves, longitudinal & transverse. In a Longitudinal wave the particles move parallel to the direction the wave is moving. In a transverse wave the particles move at right angles to the direction of wave travel.

Important Questions (1 mark): Sound - Question 20

In case of transverse wave :

Detailed Solution for Important Questions (1 mark): Sound - Question 20

The highest part of the wave is called the crest. The lowest part is called the trough. The wave height is the overall vertical change in height between the crest and the trough and distance between two successive crests (or troughs) is the length of the wave or wavelength.

Important Questions (1 mark): Sound - Question 21

In case of transverse wave:

Detailed Solution for Important Questions (1 mark): Sound - Question 21
Explanation:
Definition of a transverse wave:
A transverse wave is a type of wave in which the disturbance or oscillation is perpendicular to the direction of the wave's propagation.
Characteristics of a transverse wave:
1. Crest: The highest point of the wave above the equilibrium position.
2. Trough: The lowest point of the wave below the equilibrium position.
3. Amplitude: The maximum displacement of a wave from its equilibrium position.
4. Wavelength: The distance between two consecutive crests or troughs of a wave.
5. Frequency: The number of complete wave cycles passing a given point per unit time.
6. Speed: The rate at which a wave travels through a medium.
Explanation of the correct answer:
In the case of a transverse wave, the lowest point of the wave on the y-axis is called the trough. This is because the wave oscillates above and below the equilibrium position, and the trough represents the lowest point of this oscillation.
Reasons for the other options being incorrect:
A: The hump on the y-axis is not called a trough. A trough is a specific point on the wave, not the entire wave itself.
C: The hump on the y-axis is not called a trough. A trough is a specific point on the wave, not the entire wave itself.
D: The highest point of the wave on the y-axis is called the crest, not the trough. The trough represents the lowest point of the wave's oscillation.
Therefore, the correct answer is B: The lowest point of the hump on the y-axis is called the trough.
Important Questions (1 mark): Sound - Question 22

The wavelength is the linear distance between the:

Detailed Solution for Important Questions (1 mark): Sound - Question 22

The distance between two successive compression and distance between a compression and the adjoining rarefaction is called wavelength.

Important Questions (1 mark): Sound - Question 23

In case of transverse wave the wavelength is the linear distance between :

Detailed Solution for Important Questions (1 mark): Sound - Question 23
The distance from a certain point on one wave to the same point on the next wave (e.g. distance between two consecutive wave crests or between two consecutive wave troughs). One half the distance from the crest to the trough. Wave amplitude is a more technical term for wave height and is used in engineering technology.
Important Questions (1 mark): Sound - Question 24

The change in density/pressure of a medium from maximum value to minimum value and again to maximum value, due to the propagation of a longitudinal wave is called complete:

Detailed Solution for Important Questions (1 mark): Sound - Question 24
An undamped spring–mass system is an oscillatory system
Oscillation is the repetitive variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. The term vibration is precisely used to describe mechanical oscillation. Familiar examples of oscillation include a swinging pendulum and alternating current.

Oscillations occur not only in mechanical systems but also in dynamic systems in virtually every area of science: for example the beating of the human heart (for circulation), business cycles in economics, predator–prey population cycles in ecology, geothermal geysers in geology, vibrating strings in musical instruments, periodic firing of nerve cells in the brain, and the periodic swelling of Cepheid variable stars in [astronomy]
Important Questions (1 mark): Sound - Question 25

The number of oscillations passing through a point in unit time is called:

Detailed Solution for Important Questions (1 mark): Sound - Question 25
Answer:
The correct answer is B: frequency.
Explanation:
Frequency refers to the number of oscillations passing through a point in unit time. It is an important concept in wave motion and is measured in hertz (Hz), which represents the number of cycles per second.
Here is a detailed explanation of the concepts related to the question:
Vibration:
- Vibration refers to the rapid back-and-forth movement of an object or a medium.
- While vibrations are related to oscillations, they do not specifically represent the number of oscillations in unit time.
Wavelength:
- Wavelength refers to the distance between two consecutive points of similar characteristics in a wave.
- It is usually represented by the Greek letter lambda (λ).
- Wavelength is inversely related to frequency, meaning that as wavelength increases, frequency decreases, and vice versa.
None of the above:
- This option indicates that the correct answer is not among the given options, which is not the case.
In conclusion, the correct answer to the question is B: frequency. Frequency represents the number of oscillations passing through a point in unit time.
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