TYPES OF SOUND
(i) Audible Sound: Vibrations whose frequency lies between 20 Hz to 20,000 Hz (20 kHz).
(ii) Inaudible Sound: The sounds having frequencies above 20,000 Hz and below 20 Hz cannot be heard by the normal human ear.
PRODUCTION OF SOUND
1. A sound is produced by vibrating objects.
2. Vibration means a kind of rapid and to and fro motion of an object.
3. The sound of the human voice is produced due to vibration in the vocal cords.
4. We can produce sound by striking the tuning fork, by plucking, stretching, rubbing, blowing or shaking different objects.
5. They all produce sound due to vibration.
PROPAGATION OF SOUND
1. When an object vibrates, it sets the particles of the medium (solid, liquid or gas) around it in vibrations.
2. The particles do not travel from the vibrating object to the ear.
3. A particle of the medium in contact with the vibrating object is first displaced from its equilibrium position.
4. It then exerts a force on the adjacent particle.
5. As a result of which the adjacent particle gets displaced from its position of rest.
6. After displacing the adjacent particle the first particle comes back to its original position.
7. The process continues in the same medium till sound reaches our ear.
8. The source of sound creates a disturbance in the medium which travels through the medium.
9. The particle of the medium does not move forward but the disturbance is carried forward.
10. Sound waves require (solid, liquid, air) a medium to travel, so they are called mechanical waves.
11. Sound is transmitted through air and liquid as longitudinal waves.
12. But through solid, it is transmitted both longitudinal and transverse waves.
INTRODUCTION TO WAVES
1. The sound is produced by vibrating objects.
2. They travel from one place to another in the form of waves. Hence, the name sound waves.
WAVE AND PARTICLE MOTION OF WAVES
TRANSVERSE WAVES
LONGITUDINAL WAVES
CHARACTERISTICS OF SOUND
WAVELENGTH
TIME PERIOD
FREQUENCY
The number of compressions or rarefactions per unit time is called frequency (𝛎).
The SI unit of frequency is Hertz. The SI unit is Hertz (s−1)
v=1/T
Speed (v), wavelength (λ) and frequency (𝛎) are related as v=λ𝛎
AMPLITUDE
PITCH
VOLUME
Volume or loudness of a sound depends on the amplitude. The force with which an object is made to vibrate gives the loudness.
Higher force → higher amplitude → louder sound.
The amount of sound energy flowing per unit time through a unit area is called the intensity of sound.
NOTE AND TONE
QUALITY OF SOUND
SPEED OF SOUND
1. Sound travels through different media with different speeds.
2. Speed of sound depends on the properties of the medium: pressure, density and temperature
Speed of sound: Solids > Liquids > Gases
3. Speed of sound in air = 331 m/s at 00C and 344 m/s at 22∘ C
4. Distance travelled by a sound is 346 ms-1 at a common atmospheric temperature 250 C
5. When a source emits sound with a speed greater than the speed of sound in air, it creates a sonic boom which produces shockwaves with lots of energy.
6. They produce a very loud noise which is enough to shatter glass and damage buildings.
REFLECTION OF SOUND WAVES
ECHO
The phenomenon where a sound produced is heard again due to reflection is called an echo.
E.g: Clapping or shouting near a tall building or a mountain. To hear distinct echo sound, the time interval between original and reflected sound must be at least 0.1s. As sound persists in our brain for about 0.1s. Minimum distance for obstruction or reflective surface to hear an echo should be 17.2 m. Multiple echoes can be heard due to multiple reflections.
Note: The roof of theatre as well as the conference hall is intentionally made curved.
This is done so that the sound produced can be reflect from the walls so that the sound produced can be reached in all parts of theatre or the conference hall.
The walls of theatre are made up of soft or wooden materials to avoid echo so that it can absorb the sound.
SONAR AND RADAR
RANGE OF HEARING
1. Infrasonic sound
2. Audible sound
3. Ultrasonic sound
1. INFRASONIC SOUND
2. AUDIBLE SOUND
3. ULTRASONIC SOUND
Ultrasonic sounds are high-frequency sound having a frequency greater than 20kHz (inaudible range).
Applications:
1. Scanning images of human organs
2. Detecting cracks in metal blocks
3. Cleaning parts that are hard to reach
4. Navigating, communicating or detecting objects on or under the surface of the water (SONAR).
5. Used in “echocardiography” (ultrasonic sound are made up to reflect from different parts of heart and then make the image of the heart)
Sonar consists of a transmitter and detector mounted on a boat or ship. The transmitter sends ultrasonic sound waves to the seabed which gets reflected back and picked up by the detector.
Knowing the speed of sound in water, distance can be measured using: 2d=v×t.
This method is called echo-location or echo ranging.
REVERBERATION
DOPPLER'S EFFECT
HUMAN EAR
The ear is a sensitive organ of the human body. It is mainly involved with detecting, transmitting and transducing sound and maintaining a sense of balance is another important function of the human ear. Human ear includes:
1. The outer ear or the visible part of the ear is called the pinna.
2. Pinna collects sound from the surroundings.
3. Sound passes through a tube called an auditory canal.
4. Eardrum (tympanic membrane) vibrates in response to incident sound waves.
5. Vibrations are amplified and transmitted further by three bones hammer, anvil and stirrup in the middle ear to the inner ear.
6. In the inner ear, cochlea converts pressure signals into electrical signals.
7. Electrical signals are transmitted by the auditory nerve to the brain for interpretation.