1. Topic : Sound Made by : Kunal Aggarwal Class : IX B Roll No.: 16 Subject : Science

2. SOUND Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.

5. How does sound travel? Sound comes from a series of vibrations, and all the sounds you heard in the experiment occurred because of vibrations and energy. Sound travels in waves. When a source, or something that produces sound, vibrates, it transfers its energy to the surrounding particles causing them to vibrate. Those particles then bump into the ones next to them and so on. This causes the particles to move back and forth but waves of energy to move outward in all directions from the source. Your vocal chords and the strings on a guitar are both sources which vibrate to produce sounds. Without energy, there would be no sound. Let's take a closer look at sound waves.

6. Sound Levels

7. Compressions & Rarefactions The high-pressure region, created by a vibrating object as it moves forward, and pushes and compresses the air in front of it is called a compression (C). This compression starts to move away from the vibrating object. When the vibrating object moves backwards, it creates a region of low pressure called rarefaction (R).

8. What is a Wave ? A wave is a disturbance that travels through space and time, accompanied by the transfer of energy.

9. Types of Waves Infrasonic waves: Sound waves of frequencies below 20 Hz . Ultrasonic waves: Sound waves of frequencies below 20,000 Hz .

10. What are mechanical waves? Mechanical waves are waves which require a medium. A medium is a form of matter through which the wave travels (such as water, air, glass, etc.) Waves such as light, x-rays, and other forms of radiation do not require a medium. What are the two kinds of mechanical waves? Transverse Waves In a transverse wave the matter in the wave moves up and down at a right angle to the direction of the wave. Longitudinal Waves In a longitudinal wave the matter in the wave moves back and forth parallel to the direction of the wave.

11. Vibrations & Waves

12. Wavelength: The distance between two consecutive crests or troughs. Its unit is M & is denoted by λ . Frequency: The number of periodic oscillations per unit time of the sound wave. Its unit is Hz & is measured in ν . Time Period: The time taken by the sound wave to complete one oscillation in a medium. Its unit is S & is denoted by T . Amplitude: The maximum displacement of the particles of the medium from their mean position. Its unit is M & is represented by A . It determines loudness or softness of sound. Pitch: The shrillness of the sound produced is determined by the frequency of vibrating body. Characteristics Of Sound

13. The Human Ear The human ear is a device which converts pressure variations in air with audible frequencies into electric signals that travel to the brain via auditory nerve. The auditory parts of the human ear are given below: The outer ear is called ‘pinna’. It collects the sound which passes through the auditory canal. There is eardrum at the end of the auditory canal. When a compression of a medium reaches eardrum; it pushes eardrum inward. Similarly, eardrum moves outward when rarefaction reaches there. In this way eardrum vibrates. The vibrations are amplified several times by hammer, anvil and stirrup, in the middle ear . In the inner ear the pressure variations are turned into electrical signals which further are sent to the brain and brain interprets them as sound.

14. What Is SONAR ? SONAR is a system that uses the reflection of underwater sound waves to detect objects. This has been used to find sunken ships and schools of fish.

15. Working of SONAR The Ultrasonic waves produced by a transmitter kept in a ship are directed towards the ocean floor. The object and the ocean floor reflect these waves; the detector fitted along with the transmitter in the ship, as shown below detects the reflected waves. By measuring the time interval between the generation of the wave and reception of its echo (i.e. generation and reception of the ultrasound), and the speed of sound in water, we calculate the depth of the object.