Cheatography

# Sound Cheat Sheet (DRAFT) by Ayesha Talib

sound notes for students of class 9

This is a draft cheat sheet. It is a work in progress and is not finished yet.

### INTROD­UCTORY TERMS

 sound is a form of energy which produces a sensation of hearing in our ears. it is produced by vibrating objects. vibration is the rapid to and fro motion of an object. the matter or substance through which sound is transm­itted is called a medium. it may be solid, liquid or gas. a wave is a distur­bance that moves through a medium when the particles of the medium set neighb­oring particles into motion.

### COMPRE­SSIONS AND RAREFA­CTIONS

 compre­ssion is the region of high pressure rarefa­ction is the region of low pressure
pressure is related to the number of particles of a medium in a given volume. more density of the particles in the medium gives more pressure and vice versa.

### LONGIT­UDINAL WAVES /\ TRANSVERSE WAVES

 particles of the medium vibrate parallel to the direction of wave particles of the medium vibrate at right angles to the direction of wave waves consist of compre­ssions and rarefa­ctions waves consist of crests and troughs propagates through solid, liquid and gas propagates through solid and liquid waves cannot be polarized waves can be polarized ex. sound waves, ultrasound waves, seismic P-waves ex. light waves, radio waves, seismic S-waves

### CHARAC­TER­ISTICS OF A SOUND WAVE

 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.

### ECHO

 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.

### REVERB­ERATION

 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

 INFRASOUND ULTRASOUND 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

### SOUND WAVES /\ LIGHT WAVES

 longit­udinal waves transverse waves cannot travel through vacuum can travel through vacuum speed of sound in air is 343m/s speed of light in air is 3.108m/s have low frequency and high wavelength have high frequency and low wavelength