sound

Question 1

rarefactions

Answer 1

regions of lower air density corresponding to pressure lower than the normal atmospheric pressure

Question 2

how to read wavelength for sound

Answer 2

distance between 2 consecutive compressions/rarefactions

Question 3

speed of sound in air

Answer 3

340 m/s

Question 4

how is sound produced

Answer 4

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

Question 5

range of audible frequencies for the human ear

Answer 5

20 Hz to 20 000 Hz

Question 6

range of frequency for infrasound

Question 7

range of frequency for ultrasound

Answer 7

> 20 000 Hz

Question 8

trend between frequency of ultrasound and its power

Answer 8

higher frequency -> greater penetrating power

Question 9

speed of sound in different states

Answer 9

fastest in solids, slowest in gas

Question 10

speed of sound in air, water and glass

Answer 10

air: 340 m/s
water: 1450 m/s
glass: 5500 m/s

Question 11

what is required for the transmission of sound

Answer 11

a material medium

Question 12

what is an echo

Answer 12

the reflection of sound

formed when a sound is reflected off a hard, flat surface

Question 13

when only can you hear a distinct echo

Answer 13

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

Question 14

determine the velocity of sound by the direct method

Answer 14

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

Question 15

why cannot hear echo

Answer 15

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

Question 16

determination of the velocity of sound via calculation

for direct method and echo method

Answer 16

direct:
speed = distance/time

echo:
speed = 2distance/time

Question 17

characteristics of sound

Answer 17

loudness, pitch, quality/timbre

Question 18

loudness

Answer 18

⬆️ amplitude, ⬆️ loudness

⬇️ amplitude, ⬇️ loudness

Question 19

pitch

Answer 19

⬆️ frequency, ⬆️ pitch

⬇️ frequency, ⬇️ pitch

Question 20

quality/timbre

Answer 20

at the same note, instruments vary in quality/timbre

Question 21

use of ultrasound

Answer 21

• locate underwater objects

- medical imaging

Question 22

advantages of using ultrasound in water

Answer 22

• 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

Question 23

advantages of using ultrasound in the hospital

Answer 23

• 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

Question 24

explain how sound travels through the air to the microphones

Answer 24

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.

Question 25

explain why microphone 2 detects a quieter sound than microphone 1

Answer 25

sound waves carries energy as they travel from the source to the microphone through the air medium.
as microphone 2 is further than microphone 1 from the source of production of sound, energy would have been lost to the surroundings along the path of transmission.

Question 26

ultrasound is a longitudinal wave. describe how particles in the body move as the ultrasound passes

Answer 26

the particles in the body will oscillate to and fro about an equilibrium position in the direction parallel to the sound wave at the same frequency as the sound wave passes through them

Question 27

relation of the speed of sound and speed of light to density of the material respectively

Answer 27

speed of sound higher when material is denser

speed of light lower when material is denser

Question 28

explain why 2 similar wave pulses are shown on the oscilloscope

Answer 28

the two pulses are similar because they are both created by the same longitudinal wave of the same source

the first pulse is produced by the actual clap and the second pulse is the echo of the clap due to reflection occurring at the wall

the duration of the two pulses is the same, hence we can infer that the frequency and the pitch of the clap is the same. therefore they look similar

Question 29

compressions

Answer 29

regions of higher air density corresponding to pressure higher than the surrounding air pressure