CHAPTER- 11 SOUND
NOTES
1. Sound- Sound is a form of energy that creates the sensation of hearing in our ears.
2. Production of Sound- Sound can be produced by friction, scraping, rubbing, blowing air, or shaking an object. The object is made to vibrate, and sound is generated.
- Vibration means the rapid back-and-forth movement of an object.
- Example- In humans, speech sounds are produced due to the vibration of their vocal cords.
- A wave is a disturbance that travels through a medium and causes the particles of the medium to move, transferring the motion to adjacent particles. The particles of the medium themselves do not move forward, but the disturbance does.
- Sound waves are characterized by the motion of the particles of the medium and are called mechanical waves.
- Air is the most common medium for the transmission of sound.
- Compression (C) - A region of high pressure.
- Rarefaction (R) - A region of low pressure.
- Thus, the transmission of sound can also be seen as a disturbance in the form of changes in density.
I. Sound waves-
a) Longitudinal Waves- The transmission of disturbance in a medium can be compared to the disturbance itself. These waves are called longitudinal waves.
- Sound waves are longitudinal waves because in these waves, the displacement of the particles of the medium occurs parallel to the direction of the transmission of the disturbance.
- Example- The waves visible on the surface of water when a stone is thrown into a pond are an example of transverse waves. Light is also a transverse wave.
II. Characteristics of Sound Waves- 1. Frequency, 2.Amplitude, 3. Velocity.
- Wavelength- The distance between two consecutive compressions (C) or two consecutive rarefactions (R) is called the wavelength. Its SI unit is meter (m).
Note- Heinrich Rudolf Hertz confirmed the electromagnetic theories of J.C. Maxwell through experiments.
- They also laid the foundation for the future development of radio, telephone, telegraph, and television. They discovered the photoelectric effect as well.
- The SI unit of frequency is named after them, and it is called Hertz (Hz).
Frequency- The total number of oscillations in a unit time is called the frequency of a sound wave.
It is commonly represented by the Greek letter nu (ν).
Its SI unit is Hertz (Hz), symbolized as Hz.
- Time Period- The time taken for two consecutive compressions or two consecutive rarefactions to pass through a fixed point is called the wave's time period. It is represented by T.
The SI unit of time period is second (s).
The relationship between frequency and time period is- V=1/T
Frequency = 1 / Time Period.
Pitch- The way the human brain perceives the frequency of an emitted sound is called pitch.
Amplitude- The maximum displacement on either side of the equilibrium position in a medium is called the amplitude of the wave. It is represented by A.
For sound, the unit of amplitude is typically the unit of pressure or density.
The intensity or loudness of sound is primarily determined by its amplitude.
Loud sound - A sound with a maximum amplitude.
Soft sound - A sound with a small amplitude.
A sound with a single frequency is called a tone.
A sound produced by the mixture of multiple frequencies is called timbre or tone quality.
Noise is unpleasant to the ear.
Wave velocity- The distance traveled by a point of the wave, such as a compression or rarefaction, in a unit time is called the wave velocity.
Velocity = Distance / Time
Velocity = Wavelength / Time Period = Wavelength = 1×T
- Frequency = 1 / time period or velocity =wavelength×frequency
Note- Under the same physical conditions for a medium, the velocity of sound remains almost constant for all frequencies.
- Sound Intensity- The sound intensity is the amount of sound energy passing through a unit area per second.
III. Speed of Sound in Different Mediums-
- The speed of sound depends on the properties of the medium through which it travels.
- The speed of sound in a medium depends on the temperature of the medium.
A) Echo- If you shout loudly or clap near a suitable reflective surface, such as a building or a mountain, you hear the same sound after some time. This sound is called an echo.
- The sensation of sound in our brain lasts for approximately 0.15 seconds.
B) Resonance- The repeated reflection that causes sound amplification is called resonance.
- Excessive resonance in a hall or large auditorium is highly undesirable. To reduce resonance, sound-absorbing materials such as compressed fiberboard, rough plaster, or curtains are installed on the ceilings and walls of the hall.
C) Use of Multiple Reflection of Sound-
1. Megaphones, loudspeakers, horns, trumpets, and musical instruments like the shehnai are all designed in such a way that sound travels in a specific direction, without spreading in all directions.- Children under the age of five and some animals, like dogs, can hear frequencies as low as 25 Hz.
- Sounds with frequencies below 20 Hz are called infrasonic sounds.
- Example- Rhinoceros (rhino) (5 Hz), whales, and elephants can hear sounds in the infrasonic range.
- Sounds with frequencies above 20,000 Hz are called ultrasonic sounds.
- Example- Animals like dolphins, bats, and porpoises produce ultrasonic sounds.
6. Applications of Ultrasonics- Ultrasonics are high-frequency waves. They are widely used in industries and the medical field.
- Ultrasonics are used for cleaning parts such as spiral tubes, irregularly shaped components, electronic parts, etc., where it is difficult to reach.
- Ultrasonics are used to detect cracks and other defects in metal blocks (bodies).
- Ultrasonic waves are reflected from different parts of the heart to create an image of the heart. This technique is called echocardiography (ECG).
- Ultrasonic Sensor - It is a device that uses ultrasonic waves to obtain images of internal organs of the human body. With this sensor, images of organs such as the liver, gallbladder, uterus, kidneys, etc., can be obtained. This technique is called ultrasonography.
- Ultrasonics can also be used to break small kidney stones into fine particles.
