SOUND-QnA

Q1: What causes sound?

Sound is produced by vibrations of objects or particles.

Q2: Through which medium can sound not travel?

Sound cannot travel through vacuum.

Q3: What is the SI unit of frequency?

The SI unit of frequency is Hertz (Hz).

Q4: What type of wave is sound in air?

Sound in air is a longitudinal wave.

Q5: What is the speed of sound in air at room temperature?

Approximately 340 m/s at 25°C.

Q6: What is amplitude?

Amplitude is the maximum displacement of particles from their mean position.

Q7: What does frequency determine in a sound wave?

Frequency determines the pitch of sound.

Q8: What is the time period of a wave?

The time taken for one complete vibration is its time period.

Q9: What type of energy does sound carry?

Sound carries mechanical energy.

Q10: Name the device used to measure sound intensity.

A sound level meter is used to measure intensity.

Q11: What is echo?

The repetition of sound due to reflection from a surface is called an echo.

Q12: Define ultrasound.

Sound waves with frequency above 20,000 Hz are called ultrasound.

Q13: Define infrasonic sound.

Sound waves with frequency below 20 Hz are called infrasonic.

Q14: What is meant by rarefaction?

The region of low pressure and low density in a sound wave is rarefaction.

Q15: What is meant by compression?

The region of high pressure and density in a sound wave is compression.

Q1: Explain how sound travels through air.

When an object vibrates, it creates compressions and rarefactions in air, transferring energy from one particle to another.

Q2: What are mechanical waves?

Mechanical waves require a material medium to travel, like sound waves.

Q3: What is the range of hearing for an average human being?

Humans can hear sound frequencies from about 20 Hz to 20,000 Hz.

Q4: State two differences between loudness and intensity.

Loudness is a perception of the ear, while intensity is a measurable physical quantity; loudness depends on amplitude, intensity on energy flow per second.

Q5: What factors affect the speed of sound in a medium?

The speed of sound depends on the medium’s density, elasticity, and temperature.

Q6: What is reverberation?

Reverberation is the persistence of sound due to repeated reflections from surfaces before it dies away.

Q7: Why can sound not travel in space?

Space is a vacuum with no particles to transmit vibrations, so sound cannot propagate.

Q8: State one use of ultrasound in medical field.

Ultrasound is used for imaging internal organs and monitoring fetal growth during pregnancy.

Q9: How does temperature affect the speed of sound in air?

As temperature increases, air molecules move faster, increasing the speed of sound.

Q10: Define wavelength and give its unit.

Wavelength is the distance between two consecutive compressions or rarefactions; its unit is metre (m).

Q1: Describe an activity to show that sound needs a medium to travel.

Place an electric bell in a jar and remove the air with a pump; as air is removed, sound fades and stops, showing sound needs a medium.

Q2: Explain reflection of sound with an example.

When sound waves hit a hard surface, they bounce back, producing an echo; for example, shouting near a hill and hearing your voice again.

Q3: What are the characteristics of a sound wave?

The main characteristics are amplitude (loudness), frequency (pitch), and waveform (quality or timbre).

Q4: State conditions necessary for an echo to be heard clearly.

(i) The distance between source and reflector should be at least 17 m. (ii) The reflecting surface should be large and smooth. (iii) The time gap should be = 0.1 s.

Q5: What are the applications of multiple reflection of sound?

Multiple reflections are used in megaphones, stethoscopes, concert halls, and soundboards to amplify or direct sound effectively.

Q1: Explain how sound is produced in human beings.

In humans, sound is produced by the vibration of the vocal cords located in the larynx. Air from the lungs passes through the cords, making them vibrate and produce sound; the pitch and loudness depend on tension and length of the cords.

Q2: Describe the structure and working of the human ear.

The ear has three parts: outer, middle, and inner ear. The outer ear collects sound waves and sends them through the ear canal to the eardrum. Vibrations pass via three ossicles (malleus, incus, stapes) to the inner ear, where the cochlea converts them into nerve signals interpreted by the brain.

Q3: Discuss the differences between musical sound and noise.

Musical sound has regular, pleasant, periodic vibrations, while noise has irregular, non-periodic vibrations causing discomfort. Examples: a flute’s tone vs. traffic noise.

Q4: Explain the phenomenon of echo and its applications.

Echo is caused by reflection of sound from distant surfaces. It is used in SONAR for measuring sea depth, in echo sounders, and in architectural acoustics for sound design.

Q5: How can we reduce noise pollution?

Noise can be reduced by using silencers in vehicles, planting trees, maintaining distance from noisy zones, using soundproof materials in buildings, and enforcing noise control regulations.

Q1: How does the sound produced by a vibrating object in a medium reach your ear?

When an object vibrates, it sets the particles of the surrounding medium (like air) into vibration. These vibrating particles transfer energy to the neighboring particles, creating regions of compression and rarefaction that move outward as a sound wave. This wave travels through the medium until it reaches our ear. The vibrating air particles make our eardrum vibrate in the same pattern, and these vibrations are then transmitted through the middle and inner ear, allowing us to hear the sound.

Q2: Explain how sound is produced by your school bell.

When the school bell is struck, the metal body of the bell starts vibrating. These vibrations disturb the surrounding air particles, making them vibrate back and forth. As the particles of air vibrate, they transfer the energy of vibration to the nearby particles, creating a series of compressions and rarefactions that move outward in all directions. This vibration of air particles reaches our ears as a sound wave, and we hear the ringing of the bell.

Q3: Why are sound waves called mechanical waves?

Sound waves are called mechanical waves because they require a material medium—such as air, water, or solids—to travel. They are produced when particles of the medium vibrate and transfer energy from one particle to another. Since the motion and interaction of matter are involved in carrying the sound energy, these waves are termed mechanical in nature.

Q4: Suppose you and your friend are on the moon. Will you be able to hear any sound produced by your friend?

No, we will not be able to hear any sound produced by our friend on the Moon because sound needs a material medium like air, water, or solid to travel. The Moon has no atmosphere, meaning there are no air particles to carry the vibrations of sound. Therefore, even if our friend shouts, the sound waves cannot travel through the vacuum of space, and we will not hear anything.

Q5: Which wave property determines (a) loudness, (b) pitch?

1. Loudness of a sound depends on the amplitude of the wave. A sound wave with a larger amplitude carries more energy and is heard louder, while a smaller amplitude produces a softer sound.
2. Pitch of a sound depends on the frequency of the wave. A sound with a higher frequency is heard as a high-pitched sound (like a whistle), while a lower frequency produces a low-pitched sound (like a drum).

Q6: Guess which sound has a higher pitch: guitar or car horn?

The sound of a guitar has a higher pitch than that of a car horn. This is because the vibrations produced by the strings of a guitar are much faster, meaning they have a higher frequency. In contrast, a car horn produces slower vibrations with a lower frequency, which results in a deeper or lower-pitched sound.

Q7: Distinguish between loudness and intensity of sound.

Difference between Loudness and Intensity of Sound

Basis	Loudness	Intensity
Definition	The perceived strength or softness of a sound by the human ear.	The actual sound energy passing per second through a unit area perpendicular to the direction of sound.
Nature	Subjective – depends on the listener’s ear and perception.	Objective – a physical quantity independent of perception.
Depends on	Mainly on the amplitude of the sound wave and ear sensitivity.	On the energy flow of the wave and distance from the source.
Measurement	Not directly measured with standard instruments in basic physics.	Measured in W/m² (watts per square metre).
Example	A whisper and a shout can feel different in loudness to different people.	Intensity decreases as you move farther from the source.

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Q8: In which of the three media, air, water or iron, does sound travel the fastest at a particular temperature?

Sound travels the fastest in iron, slower in water, and the slowest in air. This happens because the particles in solids like iron are packed very closely together, allowing vibrations to pass quickly from one particle to another. In liquids, the particles are less tightly packed, and in gases like air, they are far apart, so the transfer of sound energy takes more time.

Thus, at the same temperature: Speed of sound: Iron > Water > Air

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Q9: 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?

Question:

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?

Solution:

Given:

$$ t = 3\,\text{s}, \quad v = 342\,\text{m/s} $$

When a sound is produced, it travels to the reflecting surface and back to the listener. Hence, the total distance covered by sound is:

$$ \text{Total distance} = 2d $$

Using the relation between speed, distance, and time:

$$ v = \frac{\text{Total distance}}{\text{Time}} $$ Substituting the given values: $$ 342 = \frac{2d}{3} $$

Now, solving for \( d \):

$$ d = \frac{342 \times 3}{2} $$ $$ d = 513\,\text{m} $$

Final Answer:

$$ \boxed{d = 513\,\text{metres}} $$

Therefore, the reflecting surface is 513 m away from the sound source.

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Q10: Why are the ceilings of concert halls curved?

The ceilings of concert halls are curved so that sound waves are evenly distributed throughout the hall. When a speaker or musician produces sound, the curved surface reflects the waves in many directions, allowing them to reach every part of the hall clearly.

This helps ensure that the sound intensity remains almost the same for all listeners, whether they are sitting near the stage or at the back. In short, curved ceilings improve the quality, clarity, and audibility of sound by reducing echoes and enhancing uniform sound reflection.

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Q11: What is the audible range of the average human ear?

The audible range of the average human ear is from 20 Hz to 20,000 Hz (or 20 kHz). This means that a person with normal hearing can detect sounds whose frequencies lie between 20 vibrations per second and 20,000 vibrations per second.

Sounds with frequencies below 20 Hz are called infrasonic sounds, and those above 20,000 Hz are known as ultrasonic sounds — both of which are inaudible to humans.

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Q12: What is the range of frequencies associated with (a) Infrasound? (b) Ultrasound?

Infrasound:

Infrasound refers to sound waves that have frequencies below 20 Hz. These sounds are too low for the human ear to hear but can be detected by some animals like whales and elephants.

Ultrasound:

Ultrasound refers to sound waves that have frequencies above 20,000 Hz (20 kHz). These sounds are beyond the upper limit of human hearing and are used in various applications such as medical imaging and cleaning delicate instruments.

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