- Sound is a mechanical energy which produces sensation of hearing. Sound is produced due to vibration of different objects.
- Sound wave propagates as compressions & rarefactions in the medium. Sound waves are longitudinal waves.
Characteristics of a Sound Wave
Sound waves are produced due to variations in pressure & density of the medium.
• Compression is the portion of the medium where a temporary increase in volume & a decrease in density takes place when a sound wave passes through the medium.
• Rarefaction is the portion of the medium where a temporary increase in volume & consequently a decease in density takes place when sound wave passes through the medium.
• Crest is the portion of the medium where the density (or pressure) has a value larger than its average value.
• Trough is the portion of the medium where the density (or pressure) has a value smaller than the average value.
• Amplitude is the magnitude of the maximum disturbance in the medium on either side of the mean position.
• Oscillation is the change in density (or pressure) from maximum value to the minimum value and again to the maximum value.
• Frequency enables us to know as to how many times a particular event occur in a given time.
• Time Period is the time taken for one complete oscillation in density (or pressure) of the medium.
• Wavelength is the distance between two consecutive compressions or two consecutive rarefactions.
Characteristics of Sound
• Loudness or intensity.
• Pitch or frequency.
• Quality or timbre.
Reflection of Sound
• An Echo is the phenomenon of repetition of sound of a source by reflection from an obstacle.
• Multiple echoes are heard when sound is repeatedly reflected from a number of obstacles at suitable distance.
• Megaphone, stethoscope ear trumpet, hearing aid etc are based on phenomenon of multiple reflection of sound.
• Reverberation is the phenomenon of persistence of audible sound after the source has stopped emitting sound.
Reverberation is reduced by carpeting the floor, upholstering furniture & covering the walls with some absorbing material like curtains etc.
Range of Frequencies
• Audible range of hearing of average human being is in the frequency range of 20Hz to 20KHz.
• Infrasound has a frequency below 20Hz. Ultrasound has a frequency above 20 kHz.
• Ultrasound finds application in industry, medical service & communications.
• Outer ear collects sound waves.
• Middle ear amplifies the sound waves.
• Inner ear converts the amplified sound energy into electrical energy & conveys to the brain as nerve impulse for interpretation.