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Chapter 11 Sound
We experience sound constantly in our daily lives, from voices and music to the noise of machines and nature. Sound is a form of **energy** that stimulates our sense of hearing. Like other forms of energy, sound can be transformed but not created or destroyed, following the principle of conservation of energy. Understanding how sound is produced, travels through different substances, and is perceived by our ears is the focus of this chapter.
Production Of Sound
Sound is produced by **vibrations**. When an object vibrates, it creates disturbances in the surrounding medium that propagate outwards as sound waves. Activities demonstrate this link between vibration and sound production:
- Striking a tuning fork makes it vibrate, and you hear a sound. Touching the vibrating prongs stops the vibration and the sound ceases.
- Touching a vibrating tuning fork prong to a suspended table tennis ball causes the ball to move, showing the prong is in rapid to-and-fro motion.
- Touching a vibrating tuning fork prong to the surface of water causes ripples, and dipping the vibrating prongs into water causes splashes, visually confirming the vibration.
Beyond tuning forks, sound can be produced by plucking (e.g., guitar strings), scratching, rubbing, blowing (e.g., flute), or shaking objects. In each case, a part of the object is set into vibration.
Vibration is essentially a rapid back-and-forth motion around a central position. The human voice is produced by the vibration of vocal cords. The buzzing sound of a bee comes from its vibrating wings. Plucking a stretched rubber band causes it to vibrate and produce sound.
Different musical instruments produce sound through the vibration of specific parts: vocal cords in singing, strings in a guitar or violin, membranes in a drum, or the air column inside a flute or trumpet.
Propagation Of Sound
Once produced, sound needs a **medium** to travel from its source to a listener. The medium can be solid, liquid, or gas. Sound travels through the medium by setting the particles of the medium into motion.
When a vibrating object moves, it pushes the particles of the medium next to it. These displaced particles then push their neighbouring particles, passing the disturbance along. Importantly, the particles of the medium themselves do not travel from the source to the listener; they simply oscillate back and forth around their equilibrium positions. It is the **disturbance** that travels through the medium in the form of a **wave**.
Sound waves are **mechanical waves** because they require a material medium (like air, water, or solid) to propagate. They cannot travel through a vacuum.
In air, sound propagates as variations in density and pressure. When a vibrating object moves forward, it compresses the air in front of it, creating a region of **high pressure** called a **compression (C)**. When the object moves backward, it creates a region of **low pressure** called a **rarefaction (R)**. As the object vibrates rapidly, a series of compressions and rarefactions is generated and travels outward as a sound wave.
Compressions are regions where the particles of the medium are crowded together (high density), leading to higher pressure. Rarefactions are regions where the particles are spread apart (low density), leading to lower pressure. Thus, sound propagation can be viewed as the transmission of pressure or density variations through the medium.
Question 1. How does the sound produced by a vibrating object in a medium reach your ear?
Answer:
When a vibrating object produces sound, it sets the particles of the surrounding medium (like air) into vibration. These vibrating particles transfer their energy to adjacent particles, causing them to vibrate as well. This process continues, and the disturbance propagates through the medium as a wave of compressions and rarefactions. When this wave reaches your ear, it causes your eardrum to vibrate, which is interpreted by your brain as sound.
Question 2. Explain how sound is produced by your school bell.
Answer:
When the school bell is struck with a hammer, it starts vibrating. This rapid vibration of the bell sets the surrounding air particles into vibration. The vibrations are transmitted through the air as sound waves (series of compressions and rarefactions), which travel to our ears, allowing us to hear the sound of the bell.
Question 3. Why are sound waves called mechanical waves?
Answer:
Sound waves are called mechanical waves because they require a material medium (solid, liquid, or gas) to propagate. They travel by causing vibrations of the particles within that medium and cannot travel through a vacuum (space devoid of matter).
Question 4. Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?
Answer:
No, you will not be able to hear any sound produced by your friend on the Moon. The Moon has virtually no atmosphere, meaning it is essentially a vacuum. Sound waves are mechanical waves and require a material medium to travel. Since there is no medium (like air) on the Moon, sound cannot propagate from your friend to your ear.
Sound Waves Are Longitudinal Waves
Sound waves are a type of **longitudinal wave**. In a longitudinal wave, the individual particles of the medium vibrate back and forth in a direction that is **parallel** to the direction in which the wave (disturbance) is travelling. Compressions and rarefactions are characteristic features of longitudinal waves.
A slinky can be used to model longitudinal waves. If you push and pull one end of a stretched slinky, regions of compression (coils close together) and rarefaction (coils spread apart) travel along the slinky. If you mark a point on the slinky, you'll see it moves back and forth parallel to the direction the compression/rarefaction travels.
This is in contrast to **transverse waves**, where the particles of the medium vibrate perpendicular to the direction of wave propagation (like ripples on water or light waves, though light doesn't require a medium). Sound waves in air are longitudinal waves.
Characteristics Of A Sound Wave
A sound wave can be described by its wave properties:
- **Wavelength ($\lambda$):** The distance between two consecutive compressions (peaks) or two consecutive rarefactions (troughs) in a sound wave. It is typically measured in metres (m).
- **Frequency ($\nu$):** The number of complete oscillations (changes in density/pressure from maximum to minimum and back to maximum) per unit time. It tells us how frequently the medium's particles vibrate. The SI unit of frequency is **hertz (Hz)**, where 1 Hz = 1 oscillation per second.
- **Time Period (T):** The time taken for one complete oscillation of the density or pressure of the medium. It is the time for two consecutive compressions or rarefactions to pass a fixed point. The SI unit is second (s). Frequency and time period are inversely related: $\nu = 1/T$ or $T = 1/\nu$.
The frequency of a sound wave is related to its **pitch**. A higher frequency corresponds to a higher pitch (e.g., a shrill sound), while a lower frequency corresponds to a lower pitch (e.g., a deep sound). Faster vibrations of the sound source produce higher frequencies and higher pitches.
- **Amplitude (A):** The magnitude of the maximum displacement or disturbance of the particles in the medium from their mean (equilibrium) position on either side. For sound, amplitude is related to the maximum variation in density or pressure.
The amplitude of a sound wave is related to its **loudness**. A larger amplitude corresponds to a louder sound, while a smaller amplitude corresponds to a softer sound. Loudness depends on the energy of the wave; a louder sound wave carries more energy and can travel further. Amplitude decreases as a sound wave spreads out from its source.
- **Quality or Timbre:** This characteristic allows us to distinguish between sounds of the same pitch and loudness produced by different sources (e.g., a violin versus a flute playing the same note). A sound of a single frequency is called a **tone**. Most sounds, including musical notes, are mixtures of several frequencies, which gives them their characteristic quality. Pleasant, rich sounds are often called notes, while unpleasant sounds are typically called noise.
Question 1. Which wave property determines (a) loudness, (b) pitch?
Answer:
(a) **Loudness** is determined by the **amplitude** of the sound wave.
(b) **Pitch** is determined by the **frequency** of the sound wave.
Question 2. Guess which sound has a higher pitch: guitar or car horn?
Answer:
A **guitar** typically produces sounds with a higher pitch than a car horn. This means the sound waves produced by a guitar vibrating at a higher frequency compared to a car horn.
Speed Of Sound In Different Media
Sound travels through a medium at a specific speed. The speed of sound is defined as the distance travelled by a point on the wave (like a compression) per unit time.
The relationship between speed ($v$), wavelength ($\lambda$), and frequency ($\nu$) of a wave is:
$$ \text{Speed} = \text{Wavelength} \times \text{Frequency} $$
$$ v = \lambda \times \nu $$
Since $\nu = 1/T$, we can also write $v = \lambda/T$. This indicates that speed is also the distance ($\lambda$) travelled in one time period ($T$).
The speed of sound is not constant; it depends on the **properties of the medium** (elasticity and density) and the **temperature**. Sound travels fastest in solids, slower in liquids, and slowest in gases. Generally, as temperature increases in a medium, the speed of sound increases.
Examples of speed of sound in different media (approximate values at 25°C):
| State | Substance | Speed in m/s |
|---|---|---|
| Solid | Aluminium | 6420 |
| Solid | Steel | 5960 |
| Liquid | Water (distilled) | 1498 |
| Liquid | Ethanol | 1207 |
| Gas | Air | 346 |
| Gas | Hydrogen | 1284 |
(Note the significant difference in speeds between solids, liquids, and gases. Also note that speed can vary within the same state, e.g., different solids or different gases).
For a given medium under the same physical conditions, the speed of sound remains almost the same for all frequencies.
Example 11.1. A sound wave has a frequency of 2 kHz and wave length 35 cm. How long will it take to travel 1.5 km?
Answer:
Given:
Frequency, $\nu = 2$ kHz = $2 \times 1000$ Hz = 2000 Hz.
Wavelength, $\lambda = 35$ cm. Convert to metres: $\lambda = 35/100$ m = 0.35 m.
First, calculate the speed of the sound wave using $v = \lambda \times \nu$:
$v = (0.35 \text{ m}) \times (2000 \text{ Hz}) = 700 \text{ m/s}$.
Now, calculate the time taken to travel a distance of 1.5 km (1500 m) using Time = Distance / Speed:
Distance, $d = 1.5$ km = $1.5 \times 1000$ m = 1500 m.
Time, $t = \frac{d}{v} = \frac{1500 \text{ m}}{700 \text{ m/s}} = \frac{15}{7} \text{ s} \approx 2.14 \text{ s}$.
It will take approximately 2.14 seconds for the sound wave to travel 1.5 km.
Question 1. What are wavelength, frequency, time period and amplitude of a sound wave?
Answer:
- **Wavelength ($\lambda$):** The spatial distance between two consecutive points in a wave that are in the same phase, such as the distance between two consecutive compressions or rarefactions.
- **Frequency ($\nu$):** The number of complete oscillations or cycles of a wave that pass a point in one second. It is measured in Hertz (Hz).
- **Time Period (T):** The time taken for one complete oscillation or cycle of a wave to pass a fixed point. It is the inverse of frequency ($T = 1/\nu$). Measured in seconds (s).
- **Amplitude (A):** The maximum displacement or extent of the oscillation or disturbance from the equilibrium or mean position of the particles in the medium.
Question 2. How are the wavelength and frequency of a sound wave related to its speed?
Answer:
The speed ($v$) of a sound wave is related to its wavelength ($\lambda$) and frequency ($\nu$) by the equation:
$$ v = \lambda \times \nu $$
This means the speed is the product of its wavelength and frequency.
Question 3. Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.
Answer:
Given:
Frequency, $\nu = 220$ Hz.
Speed, $v = 440$ m/s.
Using the relation $v = \lambda \times \nu$, we can find the wavelength $\lambda$:
$\lambda = \frac{v}{\nu} = \frac{440 \text{ m/s}}{220 \text{ Hz}} = 2 \text{ m}$.
The wavelength of the sound wave is 2 m.
Question 4. A person is listening to a tone of 500 Hz sitting at a distance of 450 m from the source of the sound. What is the time interval between successive compressions from the source?
Answer:
The time interval between successive compressions from the source is the time taken for one complete cycle or oscillation of the wave to pass a point. This is the **time period (T)** of the wave.
Given frequency, $\nu = 500$ Hz.
The time period is related to frequency by $T = 1/\nu$:
$T = \frac{1}{500 \text{ Hz}} = 0.002 \text{ s}$.
The distance from the source (450 m) and the fact that the person is listening do not affect the time interval between successive compressions from the source itself.
The time interval between successive compressions from the source is 0.002 seconds.
Intensity And Loudness
The **intensity** of sound is the amount of sound energy passing through a unit area per second. It is a physical measure. The **loudness** of sound, on the other hand, is a physiological response – how loud the sound is perceived by the ear and brain. While loudness is related to intensity (higher intensity generally means greater loudness), other factors related to human hearing sensitivity also play a role.
Question 1. Distinguish between loudness and intensity of sound.
Answer:
| Feature | Intensity | Loudness |
|---|---|---|
| Definition | Amount of sound energy passing through unit area per second. | Subjective physiological sensation perceived by the ear/brain. |
| Measurement | Objective physical quantity, measured by instruments. | Subjective, measured on a scale (e.g., decibels) reflecting human perception. |
| Relation to Amplitude | Proportional to the square of the amplitude ($I \propto A^2$). | Related to intensity, but also depends on frequency and individual hearing sensitivity. |
| Nature | Physical property of the wave. | Perceptual property. |
Speed Of Sound In Different Media
Sound requires a material medium to propagate, and its speed depends on the medium's properties (like density and elasticity) and its temperature. Sound travels faster in denser and more rigid media.
Question 1. In which of the three media, air, water or iron, does sound travel the fastest at a particular temperature?
Answer:
Sound travels fastest in solids, slower in liquids, and slowest in gases. Among air (gas), water (liquid), and iron (solid), sound travels the fastest in **iron**. This is because iron is a solid and is much denser and more rigid than water or air.
Reflection Of Sound
Like light, sound waves bounce off surfaces. This phenomenon is called the **reflection of sound**. When sound waves encounter an obstacle (like a wall or a mountain), they are reflected back into the same medium.
Sound reflection follows the same laws of reflection as light:
- The angle of incidence is equal to the angle of reflection.
- The incident sound direction, the reflected sound direction, and the normal to the reflecting surface at the point of incidence all lie in the same plane.
An object needs to be of a sufficient size relative to the wavelength of the sound to cause a noticeable reflection. Larger obstacles are generally better reflectors of sound.
Echo
An **echo** is the sound you hear that is produced by the **reflection of the original sound** from a surface, such as a wall, cliff, or mountain. When you shout or clap near a large reflecting surface, the sound waves travel to the surface, reflect, and return to your ears, giving you the sensation of hearing the sound again shortly after the original sound.
The sensation of sound persists in our brain for about 0.1 seconds (persistence of hearing). To hear a distinct echo, the reflected sound must reach the ear at least 0.1 seconds after the original sound is heard. This requires the sound to travel to the reflector and back in at least 0.1 seconds.
If the speed of sound in air is $v$, and the distance to the reflecting surface is $d$, the total distance travelled by the sound for an echo is $2d$ (to the surface and back). The time taken is $t = 2d/v$. For a distinct echo, $t \ge 0.1$ s.
So, $2d \ge v \times 0.1 \text{ s}$. The minimum distance to the reflector for a distinct echo is $d_{min} = \frac{v \times 0.1 \text{ s}}{2}$. If the speed of sound is 344 m/s, the minimum distance is $\frac{344 \text{ m/s} \times 0.1 \text{ s}}{2} = \frac{34.4 \text{ m}}{2} = 17.2 \text{ m}$. This minimum distance varies with the speed of sound (which changes with temperature and medium).
Multiple reflections from different surfaces can cause sounds to be heard more than once as echoes, or can cause a prolonged sound sensation like the rolling of thunder (due to reflections from clouds, land, etc.).
Example 11.2. A person clapped his hands near a cliff and heard the echo after 2 s. What is the distance of the cliff from the person if the speed of the sound, v is taken as 346 m s⁻¹?
Answer:
Given:
Speed of sound, $v = 346$ m/s.
Time taken to hear the echo, $t = 2$ s.
The sound travels from the person to the cliff and back to the person. The total distance travelled by the sound is $2 \times \text{distance to the cliff}$.
Total distance = Speed $\times$ Time = $346 \text{ m/s} \times 2 \text{ s} = 692 \text{ m}$.
The distance of the cliff from the person is half of the total distance travelled by the sound.
Distance to the cliff, $d = \frac{\text{Total distance}}{2} = \frac{692 \text{ m}}{2} = 346 \text{ m}$.
The distance of the cliff from the person is 346 m.
Question 1. An echo is heard in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is 342 m s⁻¹?
Answer:
Given:
Time taken to hear the echo, $t = 3$ s.
Speed of sound, $v = 342$ m/s.
Total distance travelled by the sound (to the reflecting surface and back) = Speed $\times$ Time = $342 \text{ m/s} \times 3 \text{ s} = 1026 \text{ m}$.
The distance of the reflecting surface from the source is half of the total distance.
Distance, $d = \frac{1026 \text{ m}}{2} = 513 \text{ m}$.
The distance of the reflecting surface from the source is 513 m.
Reverberation
**Reverberation** is the persistence of sound in a large enclosed space (like a concert hall or auditorium) due to repeated reflections of sound waves from the walls, ceiling, floor, and other surfaces. Sound waves keep bouncing back and forth, and the reflected sounds merge, creating a prolonged sensation of sound even after the original sound source has stopped.
While some reverberation can enhance the richness of sound in music, excessive reverberation in auditoriums is undesirable as it can make sounds blurred and difficult to understand (e.g., in speeches). To reduce excessive reverberation, sound-absorbing materials are used on the surfaces of walls, ceilings, and even on seats (e.g., compressed fibreboard, rough plaster, heavy curtains, padded seating).
Uses Of Multiple Reflection Of Sound
The principle of multiple reflection of sound is utilized in various instruments and architectural designs:
- **Megaphones (Loudhailers) and Horns:** These are cone-shaped devices designed to direct sound waves in a specific direction, preventing them from spreading out in all directions. The shape causes multiple reflections of the sound waves, channeling them forward efficiently towards the audience.
- **Stethoscope:** A medical instrument used by doctors to listen to sounds produced within the body, particularly the heart and lungs. The sound of the heartbeat or breathing travels through the patient's body, enters the chest piece of the stethoscope, and is guided through the tube to the doctor's ears by multiple internal reflections within the tube.
- **Curved Ceilings and Soundboards in Halls:** In concert halls, conference rooms, and cinemas, the ceilings are often curved. This shape helps to reflect sound waves towards all parts of the hall, ensuring that the sound is distributed evenly and reaches the entire audience. Sometimes, a large curved board (soundboard) is placed behind the stage to reflect sound forward across the width of the hall.
Question 1. Why are the ceilings of concert halls curved?
Answer:
The ceilings of concert halls are curved to ensure that sound waves, after reflection from the ceiling, are directed towards all corners of the hall. This helps in distributing the sound evenly throughout the auditorium, allowing the audience to hear the music or performance clearly from various seating positions.
Range Of Hearing
Not all sounds are audible to humans. The range of frequencies that the average human ear can hear is called the **audible range**. This range typically extends from about **20 Hz to 20,000 Hz (20 kHz)**.
- Sounds with frequencies **below 20 Hz** are called **infrasonic sound** or **infrasound**. Humans cannot hear infrasound. Examples include the vibrations of a swinging pendulum, sounds produced by earthquakes before the main shock waves, and communication sounds made by animals like rhinoceroses, whales, and elephants.
- Sounds with frequencies **above 20,000 Hz (20 kHz)** are called **ultrasonic sound** or **ultrasound**. Humans cannot hear ultrasound. However, many animals, such as dogs, dolphins, bats, and porpoises, can produce and/or hear ultrasound. Some moths can detect bat ultrasound to evade them.
As people age, their sensitivity to higher frequencies tends to decrease, often limiting their upper audible range to below 20 kHz.
A **hearing aid** is a device that helps people with hearing loss. It typically consists of a microphone, amplifier, and speaker. The microphone converts sound waves into electrical signals, the amplifier increases the strength of these signals, and the speaker converts the amplified electrical signals back into sound waves, which are sent to the ear to help the person hear more clearly.
Question 1. What is the audible range of the average human ear?
Answer:
The audible range of sound frequencies for the average human ear is from about **20 Hz to 20,000 Hz (or 20 kHz)**.
Question 2. What is the range of frequencies associated with (a) Infrasound? (b) Ultrasound?
Answer:
(a) **Infrasound** is associated with frequencies **below 20 Hz**.
(b) **Ultrasound** is associated with frequencies **above 20,000 Hz (or 20 kHz)**.
Applications Of Ultrasound
Ultrasound waves, with their high frequencies (above 20 kHz), have several unique properties that make them useful in various industrial and medical applications. They can travel along relatively straight paths and penetrate matter effectively.
Applications of ultrasound include:
- **Cleaning:** Ultrasound is used to clean objects with complex shapes or parts that are difficult to reach, like electronic components or scientific equipment. The items are placed in a cleaning solution, and ultrasonic waves are passed through it. The high-frequency vibrations dislodge dust, grease, and dirt particles from the surfaces, resulting in thorough cleaning.
- **Detecting Defects in Metals:** Ultrasound is used for non-destructive testing of metal blocks and other structures to detect internal cracks, flaws, or holes that are not visible from the outside. Ultrasonic waves are sent through the metal. If there is a defect, the waves get reflected back from the flaw, and this reflected signal is detected. This allows engineers to identify weaknesses in structural components. Ordinary sound waves (lower frequency, longer wavelength) would bend around such small defects, making this method ineffective.
- **Medical Imaging:** Ultrasound is widely used in medical diagnostic imaging.
- **Echocardiography:** Uses ultrasonic waves reflected from different parts of the heart to create images of the heart's structure and function.
- **Ultrasonography:** Uses an ultrasound scanner to generate images of internal human organs (liver, gallbladder, uterus, kidneys, tumours, stones, etc.). Ultrasonic waves travel through body tissues and reflect back when they encounter boundaries between tissues of different densities. These reflections are converted into electrical signals to form images displayed on a monitor or printed. Ultrasonography is also used during pregnancy to monitor fetal development and detect abnormalities.
- **Surgery/Therapy:** High-intensity focused ultrasound (HIFU) is sometimes used for therapeutic purposes, such as breaking up kidney stones into smaller pieces that can be passed out of the body naturally with urine, or for targeted tissue ablation in cancer treatment.
- **SONAR (Sound Navigation And Ranging):** Although discussed elsewhere, SONAR systems use ultrasonic waves to measure the depth of the sea and locate underwater objects (like submarines, shipwrecks, or icebergs).
Intext Questions
Page No. 129
Question 1. How does the sound produced by a vibrating object in a medium reach your ear?
Answer:
Question 2. Explain how sound is produced by your school bell.
Answer:
Question 3. Why are sound waves called mechanical waves?
Answer:
Question 4. Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?
Answer:
Page No. 132
Question 1. Which wave property determines
(a) loudness,
(b) pitch?
Answer:
Question 2. Guess which sound has a higher pitch: guitar or car horn?
Answer:
Question 1. What are wavelength, frequency, time period and amplitude of a sound wave?
Answer:
Question 2. How are the wavelength and frequency of a sound wave related to its speed?
Answer:
Question 3. Calculate the wavelength of a sound wave whose frequency is 220 Hz and speed is 440 m/s in a given medium.
Answer:
Question 4. A person is listening to a tone of 500 Hz sitting at a distance of 450 m from the source of the sound. What is the time interval between successive compressions from the source?
Answer:
Page No. 133
Question 1. Distinguish between loudness and intensity of sound.
Answer:
Question 1. In which of the three media, air, water or iron, does sound travel the fastest at a particular temperature?
Answer:
Page No. 134
Question 1. An echo is heard in 3 s. What is the distance of the reflecting surface from the source, given that the speed of sound is $342 \, m \, s^{-1}$?
Answer:
Page No. 135
Question 1. Why are the ceilings of concert halls curved?
Answer:
Page No. 136
Question 1. What is the audible range of the average human ear?
Answer:
Question 2. What is the range of frequencies associated with
(a) Infrasound?
(b) Ultrasound?
Answer:
Exercises
Question 1. What is sound and how is it produced?
Answer:
Question 2. Describe with the help of a diagram, how compressions and rarefactions are produced in air near a source of sound.
Answer:
Question 3. Why is sound wave called a longitudinal wave?
Answer:
Question 4. Which characteristic of the sound helps you to identify your friend by his voice while sitting with others in a dark room?
Answer:
Question 5. Flash and thunder are produced simultaneously. But thunder is heard a few seconds after the flash is seen, why?
Answer:
Question 6. A person has a hearing range from 20 Hz to 20 kHz. What are the typical wavelengths of sound waves in air corresponding to these two frequencies? Take the speed of sound in air as $344 \, m \, s^{-1}$.
Answer:
Question 7. Two children are at opposite ends of an aluminium rod. One strikes the end of the rod with a stone. Find the ratio of times taken by the sound wave in air and in aluminium to reach the second child.
Answer:
Question 8. The frequency of a source of sound is 100 Hz. How many times does it vibrate in a minute?
Answer:
Question 9. Does sound follow the same laws of reflection as light does? Explain.
Answer:
Question 10. When a sound is reflected from a distant object, an echo is produced. Let the distance between the reflecting surface and the source of sound production remains the same. Do you hear echo sound on a hotter day?
Answer:
Question 11. Give two practical applications of reflection of sound waves.
Answer:
Question 12. A stone is dropped from the top of a tower 500 m high into a pond of water at the base of the tower. When is the splash heard at the top? Given, g = $10 \, m \, s^{-2}$ and speed of sound = $340 \, m \, s^{-1}$.
Answer:
Question 13. A sound wave travels at a speed of $339 \, m \, s^{-1}$. If its wavelength is 1.5 cm, what is the frequency of the wave? Will it be audible?
Answer:
Question 14. What is reverberation? How can it be reduced?
Answer:
Question 15. What is loudness of sound? What factors does it depend on?
Answer:
Question 16. How is ultrasound used for cleaning?
Answer:
Question 17. Explain how defects in a metal block can be detected using ultrasound.
Answer: