general properties of waves - sound

Question 1

what is sound

Answer 1

• sound is a longitudinal wave travelling in a medium, created by a vibrating source
• medium particles are not transported away from the source
• direction of vibration is parallel to the direction of wave travel

Question 2

how is sound propagated

Answer 2

• the forward and backward vibration of a source is passed on to the air particles
• this causes alternate regions of the air particles to be compressed and extended
• compressed regions are called compressions
• extended regions are called rarefactions

Question 3

Does sound need a medium to be transmitted

Answer 3

• sound cannot travel through a vacuum
  -It needs a medium to propagate from one point to another

Question 4

Relationship between pitch, frequency, loudness and amplitude

Answer 4

Pitch is related to the frequency of the sound wave
- the higher the frequency, the higher the pitch
Loudness is related to the amplitude of the sound wave
- the larger the amplitude, the louder the sound

Question 5

Reflection of sound

Answer 5

• An echo is the repetition of a sound due to the reflection of sound
• an echo is formed when a sound is reflected off a hard, flat surface such as a large wall
• echoes obey the laws of reflection
• the angle of incidence i is equal to the angle of reflection r

Question 6

Ultrasound

Answer 6

Human beings cannot hear low frequency sounds (infrared) and high frequency sounds (ultrasound)
- ultrasound is sound with frequencies above the upper limit of the human range of audibility

Question 7

Applications of ultrasound - fishing boats use sonar

Answer 7

An ultrasonic pulse is emitted into the water and the reflected pulse is obtained.
- strength of the reflected pulses depend on the distance and characteristics of the reflecting objects
This can be used to:
- detect the location of fish
- measure the depth of the sea
Formula:
- speed of sound = 2 x depth / total time taken

Question 8

Applications of ultrasound - imaging internal organs

Answer 8

• By detecting the strength, direction and timing of the reflected pulses, an image of the internal organs can be generated
• Higher frequency ultrasound can be manipulated into thin beams, just like laser beams
• A common handheld scanner can emit and detect reflected waves
• Many emitters placed in a row each sends out a pulse of ultrasound at the same time
• From the reflected pulses in each path, the kind of tissues (e.g. fats, muscles, bones) encountered in a thin slice through the body can be worked out to construct an image of the slice

Question 9

Applications of ultrasound - pre-natal scanning

Answer 9

• Pulses of ultrasound are sent into the womb of a pregnant woman via a transmitter
• Images of foetal development are obtained via reflected ultrasound
• The strength, direction and timing of each reflected pulse are measured to allow the reflecting surface within the womb to be mapped

Question 10

Applications of ultrasound - breaking up kidney stones and cancer treatment

Answer 10

• High intensity focused ultrasound can be used to break the stone up into smaller pieces so that they can be naturally expelled in the urine; can also be used to kill cancer or tumour cells
  • Safe and non-invasive compared to surgery