Sound Flashcards
define wavelength
the distance travelled by a wave in one time period of vibration of the particle of the medium s
speed of sound depends on
- density (inverse)
- temperature (direct)
- humidity (direct)
speed of sound not affected by
change in pressure
how are electromagnetic waves formed
electromagnetic waves are formed by the periodic vibrations of the mutually perpendicular electric and magnetic fields in a plane normal to the direction of wave propagation
transfer energy as photons
define reflection of a sound wave
the return of a sound wave on striking a surface such as wall, metal sheet, etc. back in the same medium
requirement of reflection of sound wave
size of reflecting surface must be bigger than wavelength of sound wave
define echo
the sound heard after reflection from a distant obstacle after the original sound has ceased
condition for echo
- minimum distance between source and reflector in air must be 17 m
- size of reflector must be large enough as compared to wavelength of the sound wave
- intensity of sound should be such that the reflected sound reaching the ear is sufficiently loud to be audible
define reverberation
if there are repeated reflections at the reflected surface, the sound gets prolonged
use of echo
sound ranging
echo depth sounding using ultrasonic waves
properties of ultrasonic sound
- travel undeviated through a long distance
- can be confined to a narrow beam
- not easily absorbed in a medium
define natural vibrations
periodic vibrations of a body in the absence of any external force on it
the period of vibration depends on shape or size of the body
why do natural vibrations only occur in vaccum
the presence of a medium around the sound wave offers some resistance to it, and hence the amplitude does not remain constant
how is frequency related to length of air column
inversely related
how is frequency related to radius of string
inverse
how is tension related to frequency
direct
nature of natural vibrations
simple, harmonic vibrations under the restoring force
amplitude and frequency remain constant
define damped vibrations
the periodic vibrations of a body of decreasing amplitude in presence of a resistive force are called damped vibrations
rate at which energy is lost depends on nature of medium and shape and size of body
how does frictional force related to velocity of the body
directly proportional at any instant
define forced vibrations
the vibrations of a body which take place under the influence of an external periodic force acting on it
body undergoing forced vibrations are acted upon what three forces
- restoring force
- frictional force
- external periodic force / driving force
amplitude of forced vibrations depend on
external periodic force
how to keep amplitude of forced vibrations constant?
applying an external periodic force such that the driving force compensates for the loss of energy in each vibration due to the damped vibrations
these are called sympathetic vibrations
amplitude at resonance depends on what
frictional forces
define resonance
resonance is a special case of forced vibrations. when frequency of driving force on a body is equal to its natural frequency, body vibrates with increased amplitude
characteristics of sound
- loudness
- pitch
- quality/ timbre
define loudness
characteristic by virtue of which a loud sound can be distinguished from a faint one, both having the same pitch and quality
define intensity
the intensity of a sound wave at a point of the medium is the amount of sound energy passing per second normally through a unit area at that point
unit of intensity
watt per metre^2
intensity of ordinary sound and minimum sound
ordinary: 10^-6 W m^-2
minimum: 10^-12 W m^-2
intensity of sound is proportional to
- square of amplitude of vibrations
- square of frequency of vibrations
- density of air
- velocity of sound in air
loudness depends on
- intensity
- sensitivity of listener
- square of distance from source (inverse)
- amplitude (direct)
- surface area (direct)
- density of medium (direct)
- presence of resonant bodies (direct)
define noise pollution
disturbance produced in the environment due to the undesirable loud and harsh sound, of level above 120 dB from various sources such as loudspeaker, siren, moving vehicles, etc
define pitch
that characteristic of sound by which a shrill note can be distinguished from a grave note of the same loudness and quality
define quality of a sound
that characteristic which distinguishes the two sounds of the same loudness and same pitch, but emitted by two different instruments because of change in their wave forms
quality depends on
wave form
define principal/ fundamental vibration
the vibration of the lowest frequency and maximum amplitude
define subsidiary/secondary vibrations
vibrations of frequency integer multiples of principal vibrations. small amplitudes.
define music
it is a pleasant, continuous and uniform sound produced by regular and periodic vibrations
define noise
the sound produced by an irregular succession of disturbances
