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CNMS ICSE - 7 Std
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Key Terms

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Chapter: 06. Sound

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Sound: A form of energy that produces the sensation of hearing in our ears.
Vibratory motion: The motion of an object in which a part of the object moves to and fro or back and forth in a fixed pattern about its mean position.
Tuning fork: A U-shaped instrument usually made of steel, consisting of two prongs and a stem, used in laboratories for producing sound vibrations.
Larynx: The organ or voice box in humans that lies between the pharynx and the trachea and contains a pair of stretchable vocal cords to produce sound.
Vocal cords: A pair of stretchable ligaments inside the larynx that vibrate and produce sound when air passes through the narrow slit between them.
Syrinx: A ring of cartilage fixed at the lower part of the windpipe in birds that produces sound when air passes through it.
Longitudinal wave: A wave in which particles vibrate in the same direction as that of the sound.
Oscillation: The to and fro motion of particles of the medium when one full wave is constituted.
Wavelength: The length of a wave along the x-axis, which is the distance between two successive crests or troughs.
Frequency: The number of oscillations made by a wave in unit time, measured in hertz (Hz).
Time period: The time taken by a wave to complete one oscillation, measured in seconds (s).
Amplitude: The maximum displacement of a wave on either side of its mean position, measured in metres (m).
Pitch: The characteristic of sound which determines the shrillness of a sound based on the rate at which vibrations are produced.
Quality (or Timbre): The characteristic of sound which enables us to distinguish between the sounds of the same pitch and loudness produced by two different sources.
Reflection of sound: The process of bouncing back of sound on striking a surface.
Echo: The sound that is heard by the observer after it is reflected from a rigid surface.
Sonic sound: Sound within the human audible range of frequency between 20 hertz and 20,000 hertz.
Ultrasonic sounds: Sounds of frequencies higher than 20,000 Hz.
Infrasonic (or Subsonic) sounds: Sounds of frequencies less than 20 Hz.
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