All questions of Sound for Class 9 Exam

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.

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.

An earthquake produces infrasound before the mainshock wave begins. Infrasound is low-frequency sound less than 20hz.

Here, option C is correct

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.

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.

Option b

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. 

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

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.

Understanding Sound Waves
Sound waves are a fascinating topic in physics, and they have distinct characteristics that differentiate them from other types of waves.
Characteristics of Sound Waves
- Mechanical Waves: Sound waves are classified as mechanical waves because they require a medium (solid, liquid, or gas) to travel through. They cannot propagate in a vacuum, unlike electromagnetic waves.
- Particle Motion: In a sound wave, particles of the medium vibrate back and forth in the direction of the wave's propagation. This motion creates compressions and rarefactions, which are essential for the transmission of sound.
Types of Waves
- Transverse Waves: In contrast to sound waves, transverse waves involve particle motion that is perpendicular to the direction of wave propagation. An example is waves on a string.
- Electromagnetic Waves: These waves, which include light, radio, and X-rays, do not require a medium and can travel through a vacuum. They involve oscillating electric and magnetic fields.
Conclusion
Therefore, sound waves are specifically categorized as mechanical waves due to their reliance on a medium for travel and their unique particle motion characteristics. This is why option 'B', "Mechanical," is the correct answer. Understanding the nature of sound waves enhances our comprehension of various phenomena in physics and everyday life.

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

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The correct answer is (a) va = vw. This is because the speed of sound depends on the medium through which it is traveling, and the medium's properties such as density, elasticity, and temperature. So, the speed of sound in air and water will be different due to the difference in their properties, but the statement va = vw is incorrect. The speed of sound in air is approximately 343 meters per second at room temperature and atmospheric pressure, while the speed of sound in water is around 1,482 meters per second.

Because in solid and liquid molecules are closely packed whereas in air molecules are too far from each other. That's why sound travels faster in solids and liquids than in air.

Not a Character of Mechanical Waves

Introduction:
Mechanical waves are waves that require a medium to propagate or travel. These waves are produced when a source of energy causes a vibration to occur within a medium, which is then transported through the medium from one location to another. There are two types of mechanical waves: transverse and longitudinal waves.

Explanation:
The correct answer to the question is option 'D', which states that the speed of mechanical waves is comparatively higher. This statement is not true, as the speed of mechanical waves depends on the properties of the medium through which they are travelling. In fact, the speed of mechanical waves is generally much slower than the speed of electromagnetic waves.

Characteristics of Mechanical Waves:
There are several characteristics of mechanical waves that are important to understand. These include:

1. Propagation depends on the elasticity of the medium:
Mechanical waves are dependent on the elasticity of the medium through which they travel. The more elastic the medium, the faster the wave will travel.

2. Can be both transverse or longitudinal:
Mechanical waves can be either transverse or longitudinal. Transverse waves are waves that move perpendicular to the direction of the wave, while longitudinal waves move parallel to the direction of the wave.

3. Requires a material medium:
Mechanical waves require a material medium in order to propagate. They cannot travel through a vacuum, unlike electromagnetic waves.

Conclusion:
In conclusion, mechanical waves are waves that require a medium to propagate. They are dependent on the elasticity of the medium, can be either transverse or longitudinal, and require a material medium to travel. The speed of mechanical waves is not comparatively higher, as it depends on the properties of the medium through which they are travelling.

If the particles of the medium vibrate in a direction perpendicular to the direction of propagation of the wave, it is called a transverse wave. In transverse waves, the particle movement is perpendicular to the direction of wave propagation. OPTION (B) IS CORRECT.

Sound waves need a medium like air, rare gases or water to travel through. Moon has no atmosphere and sound cannot travel through vacuum or empty space because vacuum has no molecules which can vibrate and carry sound waves.....

Bcuz sound always need a medium to travel

Assertion and Reason Overview
The Assertion (A) states that sound is a form of energy that produces a sensation of hearing in our ears. The Reason (R) explains that sound waves are longitudinal waves where individual particles of the medium move in a direction parallel to the direction of wave propagation.
Analysis of Assertion (A)
- Sound is indeed a form of energy.
- It requires a medium (solid, liquid, or gas) to travel.
- When sound waves reach our ears, they stimulate the auditory system, leading to the sensation of hearing.
Analysis of Reason (R)
- Sound waves are classified as longitudinal waves.
- In longitudinal waves, the displacement of the medium's particles is parallel to the direction of the wave's travel.
- This characteristic is crucial for understanding how sound propagates.
Connection Between A and R
- Both the Assertion and the Reason are true statements.
- While the Reason explains the nature of sound waves, it does not fully explain why sound produces a sensation of hearing.
- The sensation of hearing involves complex processes in the ear and brain, which are not covered by the explanation of sound waves alone.
Conclusion
- Since both statements are true but the Reason does not adequately explain the Assertion, the correct answer is option 'B': both Assertion and Reason are true but Reason is not the correct explanation of Assertion.