Learning Sound: Basics, Types, and Impact on Everyday Life

Unit 11 SOUND

Sound happens when something vibrates and sends waves through the air. How loud or soft a sound is depends on how strong the vibration is, how big the vibrating thing is, and how far you are from it. The strength of the sound passing through a certain area is called its intensity.

Pitch is about how high or low a sound is. High-pitched sounds have fast vibrations, while low-pitched ones have slower ones. Quality is what makes different sounds of the same loudness and pitch unique.

Some sounds are pleasant, like music, while others, like jarring or harsh noises, can bother us. When these bothersome sounds get too much, it’s called noise pollution. It can mess with nature or disturb people.

We can fix noise pollution by using quieter machines, putting up barriers to block the sound, or using ear protection. Acoustic protection means using soft, porous stuff to soak up unwanted noise.

Humans can hear sounds between 20 to 20,000 vibrations per second. Anything higher than 20,000 is ultrasound, useful in medicine and finding things underwater. Anything lower than 20 vibrations per second is called infrasound.

MULTIPLE CHOICE QUESTIONS

Choose the correct answer from the following choices:
i. Which is an example of a longitudinal wave?
(a) sound wave (b) light wave
(c) radio wave (d) water wave
ii. How does sound travel from its source to your ear?
(a) by changes in air pressure (b) by vibrations in wires or strings
(c) by electromagnetic waves (d) by infrared waves
iii. Which form of energy is sound?
(a) electrical (b) mechanical
(c) thermal (d) chemical
iv. Astronauts in space need to communicate with each other by radio links because
(a) sound waves travel very slowly in space
(b) sound waves travel very fast in space
(c) sound waves cannot travel in space
(d) sound waves have low frequency in space
v. The loudness of a sound is most closely related to its
(a) frequency (b) period
(c) wavelength (d) amplitude
vi. For a normal person, the audible frequency range for sound waves lies between
(a) 10 Hz and 10 kHz ( b) 20 Hz and 20 kHz
(c) 25 Hz and 25 kHz (d) 30 Hz and 30 kHz
vii. When the frequency of a sound wave is increased, which of the following will
decrease?
i. wavelength ii. period iii. amplitude
(a) i only (b) iii only
(c) i and ii only (d) i and iii only

. REVIEW QUESTIONS

11.1. What is the necessary condition for the production of sound?

11.2. What is the effect of the medium on the speed of sound? In which medium sound
travels faster: air, solid, or liquid? Justify your answer.
11.3. How can you prove the mechanical nature of sound by a simple experiment?
11.4. What do you understand by the longitudinal wave? Describe the longitudinal
nature of sound waves.
11.5. Sound is a form of wave. List at least three reasons to support the idea that sound is a wave.
11.6. We know that waves manifest phenomena of reflection, refraction, and
diffraction. Does sound also manifest these characteristics?
11.7. What is the difference between the loudness and intensity of sound? Derive the
relationship between the two.
11.8. On what factors does the loudness of sound depend?
11.9. What do you mean by the term intensity level of the sound? Name and define the
unit of intensity level of sound.
11.10. What are the units of loudness? Why do we use a logarithmic scale to describe the
range of the sound intensities we hear?
11.11. What is the difference between frequency and pitch? Describe their relationship
graphically.
11.12. Describe the effect of change in amplitude on loudness and the effect of change in
frequency on the pitch of sound.

. ANSWERS:

1. The necessary condition for the production of sound is vibration.

The necessary condition for the production of sound is vibration. Sound production relies on several factors. Primarily, it requires a vibrating source, such as an object or material, that sets air particles in motion. This vibration generates waves that propagate through a medium, typically air. For humans to perceive this as sound, these waves need to travel to the ear, causing the eardrum to vibrate. This vibration is then converted into electrical signals, interpreted by the brain as sound. Therefore, the core condition for sound is not just vibration but the transmission of these vibrations through a medium, which allows the sensation of hearing.

2. Effect of Medium on Speed of Sound:

The speed of sound varies depending on the medium it travels through. Generally, sound travels fastest through solids, then liquids, and slowest through gases like air. This variation is due to the difference in molecular arrangement and density of the mediums. In solids, molecules are closely packed, allowing sound waves to propagate faster compared to liquids where molecules are less densely packed, and gases where molecules are widely spaced.

11.3. Proving the Mechanical Nature of Sound:

A simple experiment involves using a tuning fork and a medium like a solid table or a long string. Strike the tuning fork and place its base against the table or along the string without touching it. The sound is transmitted through the medium, showing that sound requires a medium to propagate, thus proving its mechanical nature.

11.4. Longitudinal Waves and Sound:

Longitudinal waves are where the oscillations of particles occur parallel to the direction of wave propagation. Sound waves are longitudinal in nature; they consist of compressions and rarefactions where air particles move back and forth in the same direction that the sound wave is traveling.

11.5. Sound as a Wave:

• Interference: Sound waves can interfere with each other, leading to constructive or destructive interference.
• Diffraction: Sound waves can bend around obstacles or spread out when passing through openings, exhibiting diffraction.
• Refraction: Sound waves change speed and direction when passing from one medium to another, demonstrating refraction.

11.6. Characteristics of Sound Waves:

Yes, sound waves also exhibit characteristics of reflection, refraction, and diffraction. They reflect off surfaces, refract when transitioning between mediums of different densities, and diffract around obstacles or through openings.

11.7. Loudness vs. Intensity:

Loudness is a subjective perception of sound, while intensity refers to the amount of energy per unit of area as the sound wave passes through a particular area. Loudness is influenced by intensity but also involves psychological factors like perception.

11.8. Factors Affecting Loudness:

Loudness depends on the amplitude of the sound wave, distance from the source, and the sensitivity of the human ear.

11.9. Intensity Level of Sound:

Intensity level measures the logarithmic ratio of the intensity of a sound wave to a reference level. It’s measured in decibels (dB), with the reference level being the threshold of human hearing at a frequency of 1000 Hz.

11.10. Units of Loudness and Logarithmic Scale:

Loudness is measured in decibels (dB). A logarithmic scale is used because human perception of sound intensity is not linear. A logarithmic scale better represents the wide range of intensities that the human ear can perceive.

11.11. Frequency vs. Pitch:

Frequency is the number of cycles per second in a sound wave, measured in Hertz (Hz). Pitch refers to how high or low a sound is perceived, corresponding to the frequency. A higher frequency generally leads to a higher pitch perception.

11.12. Effect of Amplitude and Frequency on Sound:

• Amplitude: Increasing amplitude increases loudness. Higher amplitudes mean more energy and a louder sound.
• Frequency: Changing frequency alters pitch. Higher frequencies result in higher-pitched sounds, while lower frequencies create lower-pitched sounds.

. CONCEPTUAL QUESTION’S ANSWERS:

11.1. Why two tin cans with a string stretched between them could be a better way to communicate than merely shouting through the air?

• The string acts as a medium for sound waves to travel more directly, reducing interference and allowing clearer communication compared to shouting through the open air.

11.2. We can recognize persons speaking with the same loudness from their voice. How is this possible?

• Recognition of individuals speaking with the same loudness is due to differences in vocal characteristics like pitch, tone, and timbre, which remain distinctive despite similar loudness.

11.3. You can listen to your friend round a corner, but you cannot watch him/her. Why?

• Sound waves can diffract around obstacles like corners, bending and reaching our ears, allowing us to hear what’s happening. Light waves, necessary for sight, travel in straight lines and cannot bend around obstacles.

11.4. Why must the volume of a stereo in a room with wall-to-wall carpet be tuned higher than in a room with a wooden floor?

• Carpets absorb sound, reducing its reflection and making the room acoustically less lively. Hence, more volume is needed in carpeted rooms to achieve the same perceived loudness as in a room with reflective surfaces like wooden floors.

11.5. A student says that the two terms speed and frequency of the wave refer to the same thing. What is your response?

• Speed and frequency are distinct properties of waves. Speed refers to how fast a wave travels, while frequency is the number of wave cycles passing a fixed point per unit of time.

11.6. Two people are listening to the same music at the same distance. They disagree on its loudness. Explain how this could happen.

• Individual differences in hearing sensitivity, perception, and subjective experiences can cause discrepancies in perceived loudness despite the same distance from the sound source.

11.7. Is there any difference between echo and reflection of sound? Explain.

• An echo is a distinct repetition of sound caused by the reflection of sound waves, usually noticeable due to a time delay. Reflection of sound is the general phenomenon of sound waves bouncing off surfaces, which might not always result in an audible echo.

11.8. Will two separate 50 dB sounds together constitute a 100 dB sound? Explain.

• No, adding two 50 dB sounds does not result in a 100 dB sound. The decibel scale isn’t purely additive; instead, a logarithmic scale is used for combining sounds. Adding identical sound levels typically results in an increase of about 3 dB, not a doubling of intensity.

11.9. Why is ultrasound useful in the medical field?

• Ultrasound is non-invasive and provides real-time images of internal body structures, aiding in diagnosis without radiation exposure, and making it valuable in various medical applications like imaging pregnancies, organs, and soft tissues.