10th icse physics chapter number 6 SOUND.pptx

Definition and characteristics of sound.

1. SOUND INTRODUCTION: Sound is the form of energy. Sound requires medium of propagation. Range of audibility is 20Hz to 20,000Hz Range below 20Hz is called Infrasonic. Range above 20,000Hz is called Ultrasonic.

2. REFLECTION OF SOUND WAVES : Bouncing back of the sound wave on striking a surface such as wall ,a metal sheet, plywood , etc. is called Reflection.

3. ECHO AND REVERBERATION Echo : The sound heard after the reflection from a distant object after the original sound has ceased Reverberation If the distance is less than 17m then the original sound mixes with the reflected sound. Due to repeated reflection the sound gets prolonged . It is called Reverberation.

4. Distinction between light waves and sound waves waves. Light Waves These are electromagnetic waves. They can travel in vacuum. They do not need medium for propagation. The speed of light wave is very high. (3x10^8m/sin air) The wavelength of light waves is very small, of the order 10^-6 These waves are transverse waves Sound Waves These are sound waves. They cannot travel through vacuum. They need medium for propagation. The speed of sound wave is very low. (330m/s in air) The wavelength of sound waves is in the range of 10^-2to 10m These waves are Longitudinal waves.

5. Condition for a formation of an echo: It cannot travel in vacuum . It requires a medium like solids, liquids and gases. It is heard only if the distance between the person producing the sound and rigid obstacle is long enough. The minimum time should be 0.1m . The echo must reach the ears atleast o.1sec after the original sound .

6. Condition for hearing the echo: Size of the reflection must be long enough as compared to the wavelength of sound wave. The intensity of sound should be sufficient so that the reflected sound should be audible . Minimum distance between source of sound and reflection must be 17m. If d is the distance of the observer from the obstacle and v is the speed of in the medium then the total distance travelled by the sound to reach the obstacle and then to come back is 2d. The time taken to hear the echo is t = total distance travelled = 2d speed of sound V Thus d = Vt = 340m/s x 0.1m = 17m 2 2

7. Uses of the echoes: 1. By bats, dolphins and fishermen. 2. By SONAR [sound navigations and ranging. 3. Echo method is used to determine speed of sound. This process is called Echo depth sound. 4.In medical for ultrasonography.

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