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3.4.4Waves

Ultrasound — Cambridge IGCSE Physics 0625 Revision Notes & Topical Questions

5 min read 10 parts Lesson 35 of 35 1 quiz

📚 Cambridge IGCSE Physics 0625 Hub / Topical Revision
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Curriculum Equation Key Wave Speed & Doppler Effect FormulasFast Exam Solution
v = f × λ | f_obs = f × (v ± v_o) / (v ∓ v_s) | T = 1 / f
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Lesson summary

3.4.4 Ultrasound — IGCSE PHYSICS notes: Describe ultrasound, how it is used to find depths and to image, and its uses in industry and medicine.Hearing range — humans hear about 20 Hz to 20 000 Hz and the range decreases with ageUltrasound — sound with a frequency higher than 20 k…

  • Transducers
  • Echo sounding
  • Other uses
  • Oscilloscope
  • Short wavelength
  • Non-ionising

Part 1 of 8What ultrasound is

Hearing range
  • Hearing range humans hear about 20 Hz to 20 000 Hz and the range decreases with age
Ultrasound
  • Ultrasound sound with a frequency higher than 20 kHz
Transducers
  • Transducers emit and receive ultrasound, and the received signal is displayed on an oscilloscope
Behaviour
  • Behaviour partially reflected at boundaries between media, with the rest transmitted

Part 2 of 8Measuring depth

Method
  • Method use the time between the ultrasound being emitted and received and its speed in the material
Equation
  • Equation depth = ½ × speed × time
  • Time is the total time from emission to receipt
  • Speed is the speed of the ultrasound in the medium
Why halve
  • Why halve the total distance is twice the depth

Part 3 of 8Sonar

Echo sounding
  • Echo sounding a pulse is sent down from the surface and reflected off the sea bed
Depth
  • Depth found from the time to return, and the distance travelled is twice the depth
Other uses
  • Other uses detect objects underwater such as shoals, wrecks and submarines

Part 4 of 8Material testing

Use
  • Use check for cracks inside metal objects and generate images beneath surfaces
Cracks
  • Cracks waves reflect back from a crack earlier than waves that continue through the object
Oscilloscope
  • Oscilloscope reflected waves show as pulses, and a bolt with no crack gives only two pulses at its start and end

Part 5 of 8Medical uses

Imaging
  • Imaging foetus in the womb and 2D images of organs, as long as they are not surrounded by bone
Method
  • Method waves are reflected at boundaries between tissues such as fluid and soft tissue or tissue and bone
  • Sweeping across an area builds up an image from the time measurements
Treatment
  • Treatment removing kidney stones
Safety
  • Safety non-invasive and believed to be harmless, unlike many other imaging methods

Part 6 of 8Why ultrasound is useful

Short wavelength
  • Short wavelength detects small features and forms narrow beams with little diffraction
Non-ionising
  • Non-ionising safe for medical use at low intensity
Gel
  • Gel applied to the skin so there is no air gap, since air reflects almost all ultrasound

Part 7 of 8Cleaning

Cleaning tanks
  • Cleaning tanks ultrasound vibrations shake dirt loose from jewellery, instruments and electronics
Reach
  • Reach cleans crevices a brush cannot

Part 8 of 8More from the specification

1Longitudinal Sound Waves
  • Sound propagates as a longitudinal mechanical wave through solid, liquid,
  • or gas media, consisting of alternating regions of high pressure (compressions) and low pressure (rarefactions) parallel to wave travel.
2Measuring the Speed of Sound
  • In a practical acoustics experiment, the time taken for sound waves to travel a measured distance between a noise source and a detector or listener is recorded and averaged to calculate speed (v = d / t).
3Pitch, Loudness, and Wave Parameters
  • The pitch of a sound is directly determined by the frequency of the acoustic wave,
    • (higher frequency corresponds to higher pitch)
  • whereas loudness is governed by the wave amplitude.
4Properties and Uses of Ultrasound
  • Ultrasound consists of acoustic sound waves with frequencies higher than the upper limit of human hearing, utilized in non-destructive testing, sonar ranging,
    • (greater than 20 kHz)
  • and medical imaging.
5Control variable
  • A quantity kept the same to make the test fair
6Average speed
  • Total distance divided by total time.
7Compression
  • Decrease in length under a squashing force.
8Rarefaction
  • Region of a longitudinal wave where particles are spread apart
9Loudness
  • How loud a sound is, set by its amplitude
10Pressure
  • Force per unit area, P = F/A.
    What the symbols mean: p = pressure (Pa = N m−2) · F = force acting at right angles to the surface (N) · A = area (m2)
11Microphone
  • Device that converts sound into an electrical signal
12Longitudinal wave
  • Wave whose vibrations are parallel to the direction of travel
13Independent variable
  • The variable deliberately changed, here time
14Dependent variable
  • The variable measured, here temperature

Key terms

TermMeaning
UltrasoundSound with a frequency above 20 kHz
TransducerDevice that emits and receives ultrasound
SonarUse of reflected sound to measure depth or find objects underwater
Non-invasiveNot requiring entry into the body
BoundarySurface between two media at which waves are partially reflected

Avoid these mistakes

1
Forgetting the factor of one half — depth is half the total distance travelled.
2
Saying ultrasound is harmful like X-rays — it is non-ionising and believed harmless.
3
Using the speed of sound in air for tissue or steel — use the speed in that medium.
4
Saying ultrasound is a transverse wave — it is longitudinal like all sound.

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