the distance between two consecutive compressions and two consecutive rarefactions is called the wavelength. SI unit is m.
the magnitude of maximum displacement in the medium on either side of the mean value is the amplitude of a wave. SI unit is that of density or pressure.
frequency is the number of oscillations per unit time. SI unit is Hz.
time taken by two consecutive compressions/rarefactions to cross a fixed point is called the time-period. SI unit is s.
speed of sound is the distance travelled by a wave per unit time.
CHARACTERISTICS OF SOUND
how the brain interprets the frequency of an emitted sound is called its pitch. pitch corresponds on frequency.
quality or timbre of sound is that characteristic which enables us to distinguish one sound from another having the same pitch and loudness.
a sound of a single frequency is called a tone.
sound produced due to a mixture of several frequencies is called a note.
noise is unpleasant to the ear. music is pleasant to hear and is of rich quality.
LOUDNESS /\ INTENSITY
is a measure of response of the ear to the sound
is the amount of sound passing each second through a unit area
SI unit is dB
SI unit is W/m2
THE LAW OF REFLECTION OF SOUND
states that the directions in which the sound is incident and reflected make equal angles with the normal to the reflecting surface at the point of incidence and the three lie in the same plane.
the repetition of a sound caused by reflection of sound waves is called an echo.
conditions for hearing an echo
time interval b/w source and reflected sound = more than 0.1s.
minimum distance b/w source and reflector = 17.2m.
intensity/loudness of sound should be sufficient for reaching the ear so as to be audible.
size of reflector must be large.
repeated reflection that results in persistence of sound is called reverberation.
ex. megaphones, loudhailers, horns, stethoscopes, ceilings of concert, cinema and conference halls [curved soundboard]
examples of sound absorbers: compressed fibreboard, plaster, draperies
RANGE OF HEARING
sounds of frequencies less than 20Hz
sounds of frequencies higher than 20kHz
rhinoceroses [5Hz], whales & elephants
dolphins, bats, rats & porpoise
humans: 20Hz-20kHz; children under 5 and dogs: 20Hz-25kHz