All questions of Sound for Class 9 Exam

To calculate the distance of the submarine from the ship, we can use the formula Distance = Speed × Time.

Given:
Speed of sound in water = 1450 m/s
Time taken for the signal to travel from the ship to the submarine and back = 4 seconds

Let's calculate the distance using the given formula:

Distance = Speed × Time
Distance = 1450 m/s × 4 s
Distance = 5800 m

Therefore, the distance of the submarine from the ship is 5800 meters.

Explanation:
The speed of sound in water is given as 1450 m/s. This means that sound waves can travel 1450 meters in one second in water.

When the ship sends a signal, it takes a certain amount of time for the sound waves to reach the submarine and then return back to the ship. In this case, the time taken is 4 seconds.

We can calculate the distance by multiplying the speed of sound in water by the time taken:

Distance = Speed × Time
Distance = 1450 m/s × 4 s
Distance = 5800 m

Hence, the distance of the submarine from the ship is 5800 meters.

Therefore, the correct answer is option 'A' - 2900 m.

Explanation:
To understand why passing the note through a vacuum is the correct option, let's first look at the properties of sound and how it travels.

Properties of Sound:
- Sound is a form of energy that travels in the form of waves.
- These waves require a medium (such as air, water, or solids) to propagate.
- Sound waves have different frequencies, which determine their pitch. Humans can generally hear frequencies between 20 Hz to 20,000 Hz.

Why a Normal Hearing Range Cannot Detect the Note:
In this scenario, the musical instrument is producing a continuous note that falls outside the range of frequencies audible to a person with normal hearing. This means that the frequency of the note is either too low or too high for our ears to perceive.

Passing the Note through Different Mediums:
To make the note audible, it needs to be passed through a medium that can transmit the sound waves effectively. Let's analyze the options provided:

1. Wax: Wax is a solid material and does not allow sound waves to travel through it easily. Therefore, passing the note through wax would not make it audible.

2. Vacuum: A vacuum is an absence of matter, which means there is no medium for sound waves to travel through. As a result, passing the note through a vacuum would not alter the sound.

3. Water: Water is a denser medium than air, and sound waves travel faster in water than in air. However, passing the note through water would not change its frequency or make it audible to a person with normal hearing.

4. Empty vessel: An empty vessel, such as a hollow container, does not provide a medium for sound waves to propagate effectively. Passing the note through an empty vessel would not make it audible.

Conclusion:
The correct option is to pass the note through a vacuum. Since sound waves cannot travel through a vacuum, the note would remain unchanged and still be inaudible to a person with normal hearing range.

Given:
- Distance between the girl and the cliff = 660 m
- Velocity of sound = 330 m/s

To find:
The time taken for the girl to hear the echo.

Solution:

Step 1: Understanding the problem
- The girl claps and the sound waves travel towards the cliff.
- The sound waves reflect off the cliff and travel back towards the girl.
- The time taken for the girl to hear the echo is the time it takes for the sound waves to travel the distance to the cliff and back.

Step 2: Calculating the time taken for sound to reach the cliff
- The distance between the girl and the cliff is 660 m.
- The velocity of sound is 330 m/s.
- Time = Distance / Velocity = 660 m / 330 m/s = 2 s

Step 3: Calculating the time taken for sound to return
- The sound waves travel the same distance back from the cliff to the girl.
- Therefore, the time taken for the sound to return is also 2 s.

Step 4: Calculating the total time taken for the girl to hear the echo
- The total time taken is the sum of the time taken for the sound to reach the cliff and the time taken for the sound to return.
- Total time = 2 s + 2 s = 4 s

Step 5: Answer
The time taken for the girl to hear the echo is 4 seconds.

Therefore, the correct answer is option 'A' - 4s.

Explanation:
Before explaining the correct answer, let's understand the terms mentioned in the options:

1. Amplitude of sound: It refers to the maximum displacement of a particle of the medium from its equilibrium position when a wave passes through it. In simpler terms, it determines the loudness or softness of the sound.

2. Intensity of sound: It is the amount of energy transmitted per unit time through a unit area perpendicular to the direction of wave propagation. It is directly related to the loudness of the sound.

3. Frequency of the sitar string with the frequency of other musical instruments: Frequency is the number of complete oscillations or vibrations an object makes in one second. It determines the pitch of the sound produced.

4. Loudness of sound: It is the subjective perception of the intensity of sound. It is related to the amplitude of sound waves.

Now let's analyze the given situation:

- The sitarist is adjusting the tension and plucking the strings of the sitar before playing in an orchestra.
- By adjusting the tension of the sitar strings, the sitarist is essentially changing the frequency at which the strings vibrate when plucked.
- Each musical instrument in an orchestra is designed to produce sound at specific frequencies, and they need to be in harmony with each other to create a pleasing musical composition.
- The sitarist, by adjusting the tension and plucking the strings, is trying to match the frequency of the sitar strings with the frequency of the other musical instruments in the orchestra.
- This ensures that the sitar produces sound at the same pitch as the other instruments, creating a harmonious blend of music.
- Therefore, the correct answer is option 'C' - the sitarist is adjusting the frequency of the sitar string with the frequency of other musical instruments.

In summary, the sitarist adjusts the tension and plucks the strings of the sitar to match its frequency with the frequency of other musical instruments in the orchestra, ensuring a harmonious musical composition.

Given data:
Distance between the boy and the wall, d = 480 m
Time taken for the echo to return, t = 2 seconds

Formula:
Speed of sound in air, v = 2d/t

Calculation:
Given that the time taken for the echo to return is 2 seconds, the total time taken for the sound to travel from the boy to the wall and back is 2 seconds. This means the sound has traveled the distance of 2d = 2(480) = 960 m.

Now, using the formula v = 2d/t, we can plug in the values to find the velocity of sound in air:
v = 2(480 m)/2 s
v = 960 m/2 s
v = 480 m/s

Therefore, the velocity of sound in air is 480 m/s, which corresponds to option 'b'.

Explanation:
When a musical note is produced by the cymbals in an orchestra, the metal plates of the cymbals vibrate. This vibration creates sound waves in the surrounding air, which we perceive as sound.

How do cymbals produce sound?
- Cymbals are metal percussion instruments that consist of two round plates made of metal alloys.
- When the plates of the cymbals are struck together, they collide and produce vibrations.
- These vibrations travel through the metal plates and cause them to vibrate.
- The vibration of the metal plates creates sound waves in the surrounding air.

Why do the metal plates vibrate?
- The metal plates of the cymbals are designed to be flexible and thin.
- When struck, one plate of the cymbal bends and creates a "warp" in the metal. This bending action stores potential energy in the plate.
- As the bent plate springs back to its original shape, the potential energy is converted into kinetic energy, causing the plate to vibrate.
- The vibrations of the metal plates produce sound waves that propagate through the air.

Comparison with other options:
a) Air columns: Air columns, such as those in wind instruments like flutes or trumpets, vibrate to produce sound. However, cymbals do not have air columns, so this option is not correct.
c) Stretched strings: String instruments, like guitars or violins, produce sound by plucking or bowing stretched strings. Cymbals do not have strings, so this option is not correct.
d) Stretched membranes: Some percussion instruments, like drums, have stretched membranes (such as drum heads) that vibrate when struck to produce sound. However, cymbals do not have stretched membranes, so this option is not correct.

Therefore, the correct answer is option 'B' - Metal plates.

Explanation:

Timbre:
Timbre refers to the characteristic quality or tone of a sound that distinguishes it from other sounds of the same pitch and loudness. It is often described as the color or texture of a sound. Every sound produced by different sources has a unique timbre that allows us to identify and differentiate between them.

Distinguishing Musical Sounds:
When it comes to distinguishing the musical sounds produced by different singers, the characteristic of sound called timbre plays a crucial role. Here's how it helps us differentiate between singers:

1. Unique Vocal Cords:
Each individual has a unique set of vocal cords, which affects the way they produce sound. The vocal cords determine the size, shape, and tension of the vocal folds, resulting in variations in timbre. These variations are responsible for the distinct qualities in singers' voices.

2. Resonance and Harmonics:
The vocal tract, including the throat, mouth, and nasal cavity, acts as a resonating chamber for the sound produced by the vocal cords. The shape and size of the vocal tract, which vary among individuals, influence the resonant frequencies and amplify certain harmonics of the sound. This amplification creates the unique timbre of a singer's voice.

3. Articulation and Technique:
The way singers articulate and use their vocal technique also contributes to the timbre of their voices. Factors such as breath control, vocal range, vibrato, and use of vocal registers (chest voice, head voice, falsetto) shape the sound produced. These techniques and articulation choices further differentiate singers based on their timbre.

4. Musical Style and Expression:
Different singers may specialize in specific musical styles or genres, which often require different vocal techniques and expression. These style-specific techniques, along with the singer's personal interpretation and expression, influence the timbre of their voice. For example, a classical opera singer may have a different timbre compared to a pop or jazz singer.

Conclusion:
In conclusion, timbre is the characteristic of sound that allows us to distinguish between the musical sounds produced by different singers. The unique vocal cords, resonance and harmonics, articulation and technique, as well as the musical style and expression, contribute to the individual timbre of a singer's voice. By listening to these timbral variations, we can recognize and differentiate between different singers.

When a wave travels through a medium, particles are transferred from one place to another. Let's explore this in detail:

What is a Wave?
A wave is a disturbance that travels through a medium, transferring energy from one place to another. It can be described as a series of vibrations or oscillations that propagate through space.

Types of Waves:
There are two main types of waves: mechanical waves and electromagnetic waves. Mechanical waves require a medium to travel through, such as sound waves or water waves. Electromagnetic waves, on the other hand, can travel through a vacuum (empty space), such as light waves or radio waves.

How Waves Transfer Energy:
When a wave travels through a medium, it transfers energy in a periodic manner. This means that the particles of the medium vibrate back and forth around their equilibrium positions, without actually moving from one place to another. As the wave passes through the medium, the particles oscillate and transfer energy to neighboring particles, causing a ripple effect.

Particle Transfer in a Wave:
The correct answer to the given question is option 'C' - particles are transferred from one place to another. Although the particles of the medium do not move from one place to another, they do transfer energy to neighboring particles. This transfer of energy allows the wave to propagate through the medium.

Example:
Let's consider a water wave as an example. When a water wave travels through the ocean, the water particles themselves do not move horizontally across the ocean. Instead, they oscillate up and down or in circular motion as the wave passes through them. However, energy is transferred from one particle to another, allowing the wave to propagate.

So, in conclusion, when a wave travels through a medium, particles are not physically transferred from one place to another. Instead, they oscillate around their equilibrium positions and transfer energy to neighboring particles, enabling the wave to propagate.

Understanding Waves
Waves are disturbances that transfer energy from one point to another, and they can be classified into two main types: longitudinal waves and transverse waves.
Types of Waves
- Longitudinal Waves: These waves move in the same direction as the energy transfer. Examples include sound waves, where compressions and rarefactions travel through a medium.
- Transverse Waves: These waves move perpendicular to the direction of energy transfer. Examples include light waves and waves on a string.
Why Slinky (Option B) Can Produce Both Types of Waves
- Longitudinal Waves in Slinky: When you push and pull one end of a slinky, you create compressions and rarefactions. This movement generates longitudinal waves, demonstrating how energy travels through the medium.
- Transverse Waves in Slinky: If you move one end of the slinky up and down, the waves travel along the length of the slinky. This movement creates transverse waves, showing energy transfer perpendicular to the direction of motion.
Why Other Options Cannot Produce Both
- Water (Option A): Water primarily produces surface waves that are a mix, but it does not generate pure longitudinal waves in the same way as a slinky.
- T.V. Transmitter (Option C): A T.V. transmitter primarily emits electromagnetic waves, which are transverse in nature, not producing longitudinal waves.
- Tuning Fork (Option D): A tuning fork creates sound waves (longitudinal) but does not produce transverse waves itself.
Conclusion
The ability of a slinky to produce both longitudinal and transverse waves under different conditions makes it a versatile tool for understanding wave dynamics in physics.