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Sound: It is a longitudinal wave that
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emanates from a vibrating source
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and requires a material medium
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Speed of sound
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In air: About 330 m/s
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In liquids: About 5 times faster (than in air)
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In solids: About 15 times faster (than in air)
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Audibility
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The human ear can detect sounds having a frequency between 20 Hz and 20 kHz.
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The human ear cannot detect infra-sounds (below 20 Hz) and ultra-sounds (above 20 kHz).
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Applications of sound and ultrasound
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Ultrasonic cleaning of machine parts
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Medical examination of the body
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Echoes are used to find depth or to detect mines or shoals of fish
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Echo: It is the reflection of sound.
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Reverberation is the effect in which you hear a prolonged sound because different echoes are reaching your ears one after the other (like in a large hall).
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Characteristics of sound
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Loudness
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It depends upon amplitude. Sounds can be soft or loud.
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Pitch
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It depends upon frequency. Sounds can be low or high.
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Quality (or timbre)
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Different audio-instruments playing the same note (same loudness and pitch) sound different.
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This is because these instruments superimpose their own additional sounds (harmonics).
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Therefore the resulting wave-forms from two different audio-instruments are different.
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Experiments
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Measuring speed of sound in air
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Method 1 is to use a stop watch and a pistol.
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Method 2 is to use an echo from a wall.
Note: In both methods use the formula: s = d / t
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Studying reflection of sound
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Use two pipes next to a wall. Sound heard is loudest when angle of incidence equals angle of reflection.
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