sound Flashcards
rarefactions
regions of lower air density corresponding to pressure lower than the normal atmospheric pressure
how to read wavelength for sound
distance between 2 consecutive compressions/rarefactions
speed of sound in air
340 m/s
how is sound produced
sound is produced by vibrating sources/bodies
they set the molecules of a medium in vibration in such a way that the energy travels out in the form of longitudinal waves
each molecule vibrates to-and-fro about a fixed point/its equilibrium position
range of audible frequencies for the human ear
20 Hz to 20 000 Hz
range of frequency for infrasound
range of frequency for ultrasound
> 20 000 Hz
trend between frequency of ultrasound and its power
higher frequency -> greater penetrating power
speed of sound in different states
fastest in solids, slowest in gas
speed of sound in air, water and glass
air: 340 m/s
water: 1450 m/s
glass: 5500 m/s
what is required for the transmission of sound
a material medium
what is an echo
the reflection of sound
formed when a sound is reflected off a hard, flat surface
when only can you hear a distinct echo
distinct echo can only be heard of it arrives at the ear with a time interval of 0.1s
minimum distance between person and the wall must be half of 34m = 17m
cuz speed travels 34m in 0.1s
determine the velocity of sound by the direct method
two persons A and B are needed. they are to stand at more than 300m away from each other on an open field. person A fires a pistol while the person B starts the stop watch when he sees the flash from the pistol and stops the stop watch when he hears the sound.
repeat the experiment and calculate the timing
speed of sound can be calculated by the formula speed=distance/time
if there is wind blowing in one direction, the 2 persons should swap positions, repeat the experiment and take the average
why cannot hear echo
if a person claps too near in front of the wall, he cannot hear the echo because the reflected sound follows too closely behind the original sound and the two cannot be heard as separate sounds
determination of the velocity of sound via calculation
for direct method and echo method
direct:
speed = distance/time
echo:
speed = 2distance/time
characteristics of sound
loudness, pitch, quality/timbre
loudness
⬆️ amplitude, ⬆️ loudness
⬇️ amplitude, ⬇️ loudness
pitch
⬆️ frequency, ⬆️ pitch
⬇️ frequency, ⬇️ pitch
quality/timbre
at the same note, instruments vary in quality/timbre
use of ultrasound
- locate underwater objects
- medical imaging
advantages of using ultrasound in water
- ultrasound not confused w other natural sounds in the water because the ultrasound detector does not respond to ordinary sound frequencies
- high frequency, short wavelength -> more easily concentrated in a narrow beam -> penetrate greater depth
- using waves of short wavelength -> smaller sized objects/details can be located -> improve resolution of image
advantages of using ultrasound in the hospital
- much safer than x-rays which damage cells by ionization
- can be used continuously w/o any injury to the patient
- can measure the depth of an object below the body surface from the time delay of echo
- can detect difference between soft tissues in the body which x-ray cannot; can be used to detect tumors/lumps inside the body
explain how sound travels through the air to the microphones
the layer of air molecules next to the sound source is set into to and fro vibration about its equilibrium position, parallel to the direction of travel of the sound wave at a certain frequency.
the to and fro movement of the layer of air creates a region of compression and rarefaction.
the series of compressions and rarefactions move outwards from the sources to the microphone/sound will transmit as a series of compressions and rarefactions.
the source, medium and receiver will all vibrate at the same frequency.
